Just bought a bi-colour rope and found little bumps for about 30cm where the two colours meet... is this normal for bi-colour ropes??

No, bumps in new ropes are not normal... what make of rope is it? How big are the bumps? Are the bumps visible or can you feel them only? (If the bumps are visible, send me a pic please!)
Have you climbed on the rope? Has anything extraordinary occurred with/around/etc that might influenced these bumps? (do you have measles!?)

Your rope does not sound right at all (although I have not used or handled a bi-colour rope before)
I suggest you take the rope back to where you bought it from and ask them about it. And don't use the rope in the mean time!

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Climb ZA - Administrator