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You can reject the latest one as being "not as described", but they can at their discretion send you another one which is as described (i.e. the right colour). They might not be able to do that economically, and you can't insist that they do, but their only other option is to take it back and give you a full refund, unless you voluntarily make an alternative offer which is better for you and which they also prefer.
You might have a case that the amount of time it has taken for them to replace the bike is unreasonable and you should get a full refund for that reason, but that's a matter of argument rather than being cut-and-dried as the other options are.
I originally bought the bike in December 2016, and then I received this one on Monday.