I'm reading a book about the Photographer Dorothea Lange and her work during the depression era and beyond as part of my photography course. I came across a photograph which she had taken in late '30s Mississippi. It's of the front of a small cinema, ornately decorated and adorned with the words:

'Theatre. For colored people only.'

Okay, typical of the era of segregation BUT why isn't it spelt Theater instead of Theatre???? I thought the former was more common in the US whilst the latter is often seen in Europe. If it is a case of a transition from one word to the other then did this take place in the '30s? And if so, why then?? What surprises me most is its inclusion with a clearly Americanised 'colored'. Have these words evolved into American English at different times?