Right, I'll step in here. Normally I wouldn't bother, 'cause I'm lazy, and this is practically a non-issue, but since Deepstar is apparently actively using an Amiga (see signature) I'm gonna be nice
That particular part of the HUD cannot be set from the options screen, and is basically hardcoded to the red it is in. It's no value defined in the HCF settings.
So, there. For the colour to be changed, you need someone to code in support for setting that colour like the other HUD parts. Or alternatively, you could hard code another colour value (which would be pretty stupid, however).