1. How about painting the wall a new color?

2. How about we paint the wall a new color?

(Are both grammatical?)

Both are slang, somewhat, but the first one is more commonly used.

'How about painting the wall a new color?' is addressing one person asking a question to a separate individual. 'How about we paint the wall a new color? is referring to the person asking the question who would like to help the individual with the painting.

Yes, both sentences are grammatically correct. However, the difference between them lies in their usage and context.

1. "How about painting the wall a new color?" - This sentence is a suggestion or recommendation. It is like saying, "What do you think about the idea of painting the wall a new color?" Here, "painting the wall a new color" is a gerund phrase functioning as the object of the verb "about."

2. "How about we paint the wall a new color?" - This sentence is also a suggestion, but it includes the word "we," indicating that the speaker is proposing to take part in the activity. It can be interpreted as, "What do you think if we paint the wall a new color?" Here, "paint" is the main verb, and "the wall a new color" is the direct object.

Both sentences convey a similar meaning, but the second one includes the speaker as an active participant in the action.