If memory serves correctly, this was the original concept of Zero before it was changed into the current one, red and blue (the dark red color is the same as normal so only a single red color used), but instead of called Zero, they named him "Ultraseven Ax". This form also begs the question, if full red colored Zero exist, will there also be full blue ? Only time will tell. Also we never gets a glimpse of Zero's mother but she's definitely come from blue color tribe.