Tell us how it came...what kind of potting mix? Other than the color, does the plant appear to be in good shape? What condition is the root system in?

I'd advise that you call or email the vendor from which you bought your plant to see what they suggest about both the color and the fertilization. All container grown plants require fertilizer to maintain normal, healthy growth. The goal should never be to push a plant into accelerated growth, which isn't good for their long term health.

It came in what looks like miracle grow potting mix with a little added perlite.
Everything else looks good, nice firm stem and leaves.
Roots look good.
I already emailed her, waiting for a response, just wanted to get a couple opinions :)

maybe it was 'in the darkness' for too long & lost color?
If there is any problem with the plant, not sure that feeding it would help...Needs to get better first.

Flower Baby, shipping, shocks the heck out of plants.

Do you know how many days/weeks your Begonia was in transit?

Were days hot between shipping from nursery to your house?

I'd hold off fertilizing. Some nurseries fertilize plants.
When you talk to the owner, ask if Begonias were fertilized.
Some nurseries add 3 or 6-month pellets/ball fertilizers.

If pellets were recently added, you should see them mixed in the soil. Older pellets eventually deplete.

The yellow leaves will fall off...but since roots and stems are healthy and sturdy, new leaves should sprout.

I loved ordering plants online, Flower Baby, but depending on nursery and time of year, chances were plants wouldn't look as pretty/healthy as they did in the photo.
The risk of ordering. But, most of the time, well-worth it. Toni

Did your Begonia perk up, FB?