What a fun little space! (That's tip #1, consider it a fun place to get to call your own! Think like a kid a their grandparents' house!)

Before you sit facing the wall, is it possible to use a standing desk or bar-height desk and be able to look out the window?

Assuming a standing desk isn't an option, there are two main things:

First, give your flat wall some depth. Some possibilities: Use a fabric bulletin board. Make a gallery wall of empty, chunky frames all painted identically. Put a series of mirrors the same size and height as your window along the back wall. Or you can create some combination of these.

Second, make the lighting fun. Could you put a lamp with a stained glass shade up in the window nook? That would catch the daylight to spread color in the little room. Or it could just be a glass art piece by the window. Could you put an accent light or container with string lights on top of the opposite shelves? That will pull some focus up there and help the room seem bigger. Make sure your desk lamp gives you plenty of good working light and is beautiful to sit with too. You don't want a functional light that's ugly or glaring. If you're really whimsical, you could do string lights criss-crossed and draping down from your ceiling.

In terms of color, I would look for an accent color in your master bedroom that makes you feel like doing your work, whether that's a bubbly or zen color. Use that accent color to wrap your office. Then your accent color will really pop in your bedroom too. (You might install curtains across your nook in case you want to close up shop or downplay a bright color.)

Hope some of that helps! Best of luck.

Here are a few photos to help you imagine...

Eclectic Home Office · More Info

Painted Maple Corner Office - Armonk, NY · More Info

Green · More Info

House for Two Artists · More Info

квартира на Новой Риге · More Info

Crescent Moon · More Info

Do you think a dark desk or white desk will make the room feel bigger and more open?

I'd look for a white desk. Be sure to incorporate a desk lamp for soft lighting, or wall sconces.

What about considering a wall mural?

Here another idea...

There are stained glass hangings that you could hang in the window. White shades will give you more light.

You don't want to stare into a light fixture. If, like most of us, you are right handed, you'll need your light over your left shoulder and/or above you and/or behind you. Seriously consider a pair of brass swing arm lamps hung on the longer wall so you're not taking up desk space for lamps.

Is the base non-cabinet beneath the shelving in the right niche the top of a stairwell?

Reaching over a desk to get to items on those shelves will be a chore. You might consider replacing those shelves with a pair of wide vertical drawers with shelves within them. Alternately, you might consider a "drop down" wall desk -- something you could lift out of the way so you could stand where you need to stand in order to reach the shelves, with lights hung above it or built into it .

https://www.ashleyfurniture.com/p/ken-wall-mount-laptop-desk/H6000014-10.html?mrkgcl=1069&product_id=H6000014-10&google_pla=true&&gclid=EAIaIQobChMIjNO9rea55wIViZWzCh3Vxw4pEAQYASABEgIuuvD_BwE&gclsrc=aw.ds

http://bagitau.net/big/

https://www.wayfair.com/Ebern-Designs--Kabir-Floating-Desk-X112278486-L32-K~W001167375.html?refid=GX263456939659-W001167375_729142082&device=c&ptid=649320624230&network=g&targetid=pla-649320624230&channel=GooglePLA&ireid=82546593&fdid=1817&PiID%5B%5D=729142082&gclid=EAIaIQobChMI29X85-W55wIVCaGzCh32Zg-IEAQYBiABEgI5vvD_BwE

Or a drop down version.

I like the look of this first butcher's block wood one:

https://www.etsy.com/listing/680545889/wall-mounted-pc-table-fold-down-desk?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=drop+down+table&ref=sr_gallery-1-14

and this one that is both shelf and drop table.

https://www.pinterest.com/pin/258112622370437492/?lp=true

https://www.pinterest.com/pswr/drop-down-desk/

You might consider an elongated narrow drop leaf breakfast table. It doesn't, however, add storage.

https://www.google.com/search?q=rectangle+drop+leaf+kitchen+table&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjG8rKY6bnnAhWHY98KHQNKDvYQ_AUoAnoECA0QBA&biw=1366&bih=628#imgrc=KDl9myCTtx_DLM

There are ironing board style cabinets that could enable your to have a narrower elongated drop down table top -- perhaps leaving room for two chairs.

https://www.google.com/search?q=drop+down+wall+desk&tbm=isch&ved=2ahUKEwidgPLn5bnnAhUJQlMKHb7jCW4Q2-cCegQIABAA&oq=drop+down+wall+desk&gs_l=img.3..0j0i8i30l2.138831.141865..142198...0.0..0.120.1281.17j2......0....1..gws-wiz-img.....0..0i67j0i131j0i30.5zWQjq5Tr2w&ei=NGI6Xp2WGomEzQK-x6fwBg&bih=628&biw=1366#imgrc=DCbkaIaKkxT80M

If you prefer a more conventional table or desk, consider choosing a round one, perhaps with wheels so its more easily moved about and you're not bumping sharp corners..

I'd personally prefer light wood finish rather than painted desk/shelf and/or wall shelves but since you already have white painted shelves, unless you're replacing those shelves (need to be deeper) just paint them all in your favorite color -- not necessarily the wall color. You could paint the wall of the niche a light shade of your favorite color and the board/desk/shelves a darker shade of the same color -- or vise versa.

A mural on all/most of the walls could end up being a bit too "busy". There are posters used to create faux windows -- you might consider a faux window cabinet door for some of your storage.

https://www.wall26.com/wall26-beautiful-garden-backyard-view-from-inside-a-window-p-32247

Something else you might consider is utilizing a table height wood filing cabinet set just inside your bedroom as part of your mini-office and not crowd the niche as much for your storage. Choose the kind with two file drawers and a top drawer for your pens, etc. That way a sofa table that is wider but not as deep work well for your office desk.

https://www.homedepot.com/canvas/pep/Linon-Home-Decor-Titian-Antique-Tobacco-Desk-86154ATOB-01-KD-U/205942118?mtc=Shopping-BA-F_HDH-G-D59-59_34_INTERIOR_FURNITURE-MULTI-NA-Feed-PLA-NA-NA-Home_Office&cm_mmc=Shopping-BA-F_HDH-G-D59-59_34_INTERIOR_FURNITURE-MULTI-NA-Feed-PLA-NA-NA-Home_Office-71700000048685358-58700004834194635-92700046771714000&gclid=EAIaIQobChMIlemZyey55wIVCZyzCh3hkwPnEAQYAyABEgIsUvD_BwE&gclsrc=aw.ds

I'd actually prefer furniture rather than a built in unless, perhaps, I was choosing the wall hung drop down or lift up desk that includes storage.

Thanks for all the suggestions above. I will buy a white desk to make the space seem more airy. What kind of light can I hang in the ceiling to give it open feel. I like simple modern designs. Links would be helpful!

Since this is open to your master, can you show photos of the decor there?

I love the little nook... are you sure you want it to be a workspace? I would never get to sleep if I had that distraction...

but i do love my wine/coffee bar in our master.

Since your nook is so small, consider a built-in desk with cabinets above. And yes, go with white since lighting is limited. Don't cover the round window, you need all the light you can get. Have you considered a sliding barn door to close off your work space from your bedroom? This would be an ideal spot for a barn door. The opening of your nook may be a little wide unless the wall where the barn door would slide to is large and empty. If not, you may have to make the nook opening narrower.

If you want a ceiling light in there I would look for a flush or semi flush mount with a diffuser at the bottom so you don't get odd shadows. You will also want a small table lamp with a white shade to provide light on the desk. I wouldn't put any shelving above the desk since you have the shelves in the side of the space.

Questions for you to ask yourself.

Do you already have a box for an overhead light? Is it centered? Will the light be over or in front of you or are you going to end up creating a shadow on your workspace with an overhead light where it is located?

Have you spent any time in the nook to see if it is overly hot or cold -- or does it stay the same temp as your bedroom?