Contact them and politely explain that by not providing a colorblind option, they are technically in breach of the 2010 Disability and Equality Act. I say technically because as per usual the definition of whether colourblindness is a disability is a case of pot luck.
The Act basically makes it illegal for any service or product to be unusable or very difficult to use by a disabled person. Any web developer worth their salt knows this one inside out, since it's been a big issue since the early 2000's.
My friend is colourblind so I know how annoying it can be. He gets frustrated when I forget and tell him to "shoot the red one" or something.
On a side note, Team Fortress 2 has a colourblind option which changes effects like burning and Uber so they're not so reliant on colour.