in deep water, red appears dark blue to black.
yellow on the other hand, carries well under water.
well, that's what i know at least from inferring.
Cirrhilabrus marjorie appears dark blue in deeper water, while the yellow spot on Cirrhilabrus lyukyuensis and the yellow streak on Cirrhilabrus randalli carries well in deeper water. Oceanic species such as C. randalli from Rowley shoals use the yellow colouration to keep in touch.
Not sure how true this is, it's from some books and sources. Do correct me if i'm wrong.
But if your angel is expressing interest in red colouration in daylight, then perhaps it can really see the colour red! and it's going nuts for it haha.