During the period of racially segregated bathrooms in the US, what were the rules about white people using colored bathrooms, for example, as a protest against segregation?

by mpierre

Could a white supporter of the civil rights movement choose to use the colored bathrooms as a form of protest?

How would it be received by the colored people? Would it be seen as encroaching on their space or on the contrary, as a rejection of the segregation?

On a side note, was there a lot of standard differences between colored and white bathrooms? I mean, where the colored ones less maintained?

retailguypdx

And as an additional nuance to the question, would there be a stigma if a white person used a colored bathroom simply because the line was too long at the white one?