Are you sure about this? I have a dark blue color that has this same problem.
Edit: Actually, on second thought I think you're right. My phone has an OEM color called Verizon. I replaced the light theme version of the color with black, and replaced the dark themed version of that color with blue.
It looks like even when I'm using the blue on dark theme, the email client is using the black on light version, since the email client always uses the light theme. So that makes sense. Cool, I just wish my phone was still interop unlocked so I can make changes.
Sent from my HTC Trophy using Board Express