I suppose then blue must be a bit better than the red. Obviously a CHE would be the move when you can afford it, but for now I would go with blue light. What kind of enclosure do you have? Is it possible that there is too much ventilation from either an AC, fan, etc.? I have had issues keeping temps up at night but the lowest I've dealt with is the 75-78 range so nothing too terrible. Please keep me updated on what you decide to do! Best of luck bringing the temps up at night!
Exo terra with the top covered in tin foil with enough space for the light to sit on the mesh