You could consider chocolate brown to complement the espresso furniture.

perfect!

As you are lengthening your curtains/drapes, please avoid adding too
much -- that sloppy drag-the-floor fad looks truly awful and using a vac
near it a real chore.

Chocolate brown? Nope -- dark and depressing and too obviously a patch.

Instead, pick a pattern that coordinates with your curtains. With silver gray and tan, consider either of the three as a background color with one of the other two as a pattern.

Suggest you consider adding the color to the TOP as a valance but attached to the curtains, perhaps
even extending the valance down each side of the curtains/drapes

http://4.bp.blogspot.com/-FeasbcG4sL4/T77wX_Se-iI/AAAAAAAABOw/95Yl_3AE4Sc/s1600/IMG_8855.JPG

http://harold437.tripod.com/webonmediacontents/1485371.jpg?1455153699114

and do so by creating a
rod pocket rather than adding a rag at the bottom -- and don't use a
drastically different color; instead, pick a fabric that compliments the
existing fabric, perhaps having the same color within the fabric
pattern.Silver and beige geometric:

https://singularity-buyfabrics.s3.amazonaws.com/products/46804/images/46804_08967757-f168-4b78-a36e-de4f702269c0.jpg

Curtain Fabric - Acacia Beige/Silver Fabric with Silver Embroidered Swirl!

https://s-media-cache-ak0.pinimg.com/736x/bf/a9/1c/bfa91c30f343d8522175b433e231ecff.jpg

Antique silver and straw print.

http://judytopkis.com/fabric2-05/floral_ydg_beige2.jpg

between you and me, i love the "sloppy drag-the-floor" timeless look. and it is not outdated as some say, because all the places still have them. i think you just need to know how to use clothes pins. Lets see now that i have shown my awfulness, what were we saying? oh yes, how about using sheer at the top to let light in. saw recently very cool.

William Hefner Architecture Interiors & Landscape · More Info

I would probably add a soft print in a color that coordinates with the stripe. It is easier to add at the bottom than the top. I might add a smaller band of the same fabric, overlay-ed not inset, either down the sides or across the body at another location. I would also use the fabric again on pillows somewhere else in the room. MEASURE very carefully keeping everything square is the difference between looking professional and slipshod.

I would consider lengthening the curtains by adding fabric to the top portion! I think a patterned fabric would add a lot of interest and make the drapes look more custom! Maybe an espresso colored pattern?

oh, 2 great places for fabric. Spoonflower.com - artist designed. fabric. com all the popular ones.

I prefer the look of an inset near the bottom. The advantage of an inset is that you don't need to refinish the top or bottom hems.

My Houzz: DIY Love Reforms a Dated Cape Ann Home · More Info

just make 2 new ones?

Consider a darker drapery rod, put the dark fabric on the bottom,, keep the bottom off the floor a bit as dust clings and shows on dark fabric.

Since the drape has grommets ( very in right now) I think add to the bottom. Unless you are a very skilled seamstress, you might mess up trying to add closer to the top. You have lots of good ideas to consider.

Please post the drapes when you have finished so we can see your room!

Options of where to sew it -- please post photo of your flooring? Sometimes the strip connects with color of the flooring... houzz photos have shown that.

Does that store sell another color of the same fabric -- in valance or scarf -- use that fabric.