What is the meaning of まっちろけ? > (context: it's lunch) or > (context: scene of an accident) Does it have something to do with , masshiro? I think it may be some sort of obscure slang I don't know about, because I can't find any information on the internet and I don't see how pure white (masshiro) could apply to either of the examples.

is indeed a colloquial and/or jocular way of saying {}{}, which means "pure/all white".

{} would refer to a bento consisting of rice (which is white) and other things that are mostly very light-colored. Upon hearing that phrase, most Japanese-speakers would think of a visually unappetizing bento.

Finally, without more context or an explanation of the situation, I could not tell what might mean. It could mean that the speaker has a blurred memory of the accident, but I really should not be speculating. We do say to mean "My mind went blank."