The colors shouldn't be washed out, the gallery doesn't change any of the image properties. Try checking your JPG quality settings when you save the image. If you're using Adobe Photoshop, use Save As (not Save For Web) and I recommend using the highest JPG quality setting (12).
No I'm not using Save for Web. I'm not using highest quality as not to make the file too big, however the difference is not between the psd file and the jpg but between the jpg I saved to my computer (and uploaded) and the file I'm viewing in the gallery. When I originally uploaded and noticed the colour difference I actually deleted the files I had uploaded and saved the psd as jpg to a higher quality to see if this was the problem but the difference was still there. This has happened only with these particular files (cover and stomp) - I hadn't noticed it before with any other files I uploaded.