Could she be color blind?

my daughter is 2 and half now. she has been starting to learn her colors and is doing great. the only color she has a problem with is red. she calls green green and brown brown knows all her other colors blue orange yellow pink purple no problem but she calls the color red green. ive called her doctor and she says she will need to run some test. i know color blindness is very rare in girls but my father is color blind. could she be color blind or am i just being paranoid? any help or ideas will be more then welcome. thanks