ELI5 Shampoo - all colors of shampoo foam white, why?

ELI5 Explain Like I'm 5: Bite sized answers to stuff you should know about - in a mini podcast

Why do adult shampoos sting your eyes while kid shampoos are eye friendly? What is the difference between shampoo, soap and shower gel? Why is it that no matter the color of the shampoo, the foam is always the same - white? If shampoo strips away oil and conditioner adds oil, how are 2 in 1 shampoo + conditioner products possible?

... We explain like i'm five!

Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: jackthejokey, p33k4y, jesshashobbies, fawkesfan, train_of_thoughts, zeekidc2, war-gear2004, squeezypoofs, droccafella03, kobusa, lumpywon, nokvok & omapuppet.

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