Colorism is a reason, but it is not the main reason. Too many are making it seem like colorism is the main reason, when it is more an ancillary reason, an important part for sure, but not the main reason for success. Zendaya light-skin helps, but if she did not have the acting chops she would just be another bi-racial female who wanted to be a movie star. It is in a similar vein to beauty. Beauty makes the path easier, but only skill will allow you to actually succeed (unless you have nepotism in your favor).