what about other colours? Yellow? Orange?
A yellow-Amber is possible, with the right amount of Eumelanin (aka, almost none and all brown, with a decent amount of variation in various parts of the iris to get the desired effect.) Orange, I just don't know.
As it is, really thinking about it, Pheomelanin-rich 'Red' eyes would generally range from a series of Greyish-pinks like
#DEA5A4 (which would suck as much as having extremely pale blue eyes does IOTL) and violets (like
#B57EDC) to very dark reds like
Japanese Carmine and web-safe
Maroon. Even then, the actual basic color is also dependant on the levels of both kinds of Eumelanin (brown and black) in the iris. And then Ambient light levels combine with that to produce the observed color.
And as a fun fact, under certain light conditions, light blue and grey eyes can tend to appear violet or pinkish anyway.
EDIT:
Most people with blue or green eyes have elevated pheomelanin already, but this structural color overrules any reddish tint.
Which is why you'd need much more of it, and much less Eumelanin. Green Eyes are actually caused by a stroma that is fairly brown Eumelanin-light, with very little black Eumelanin to go with it, and the blue-tone from Rayleigh scattering.
Any 'Red' Eye gene would likely produce reduced levels of eumelanin production in the stroma while elevating pheomelanin production, which would create different tones than we see now.
(But there's no way to really test this without experimentation on cats or something.)