That is indeed strange. For HTML colors it really shouldn't matter the computer you are using. Normally the main issue when changing servers is missing fonts: Normally the server has less fonts installed than the dev machine and this can cause problems when exporting since FlexCel can't find the needed fonts.
But I've never seen something like it for colors, and I can't imagine why colors would not show up in the server but yes in the dev machine. Do you have any extra info we can look at? Maybe email me the template and generated files (both in the server and the dev machine) so I can take a look and maybe figure out something? (my email is adrian@tmssoftware.com)
I've got you files, and I've been trying out to figure out what is going on, but I can't still find a reason why the colors wouldn't show up in the server, but yes in the dev machine. Are you sure the tags are the same in both machines? Note that in Delphi in many places components use colors like "clRed" as valid HTML, but FlexCel will only accept "red" which is the one in the HTML standard. Can you run the report with html off, and let me know the exact html you are entering into the cell?