my guess is that in the manga, they wanted her to have purple hair, and when they looked at it in the anime, they decided that blue might be better to go with. that is my opinion. i have been curious about that too.
I have some pages in the manga colored سے طرف کی Toriyama and I can say that there are many colors that do not match the anime, probably the TOEI اندازی حرکت had decided to change them because with the original colours the عملی حکمت would have an older look. For example nam have a گلابی dress in manga :)