Hi Heidi, yellow is not usually a worrisome color, but orange or pink can be. Since you are still fairly early in the process, I think it's fine to continue but I wouldn't use any discard until your starter is bubbling nicely, rising at least a bit, and has a pleasant aroma. If you continue to see yellow spots as the starter progresses, it might be best to start over, but I suspect you won't. 

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