To give another deviant a direct link to this FAQ answer, use the following code in your comment or forum post:
I submitted an image to deviantART but the colors look different then they did on my computer or the image looks blurry or pixelated. Why is this?
One of the main reasons colors change when a piece is submitted because the piece was saved with a color profile embedded. Since browsers cannot read this color profile it will not be displayed along with your image. Re-saving your image without a color profile embedded should rectify this issue.
The second reason colors could look off or make your image appear blurry or pixelated is because it was not saved in the highest quality possible or in the wrong format. Always be sure to save your image to the highest quality possible and use correct formats where possible, this will ensure the image is viewed in the way you wish.