Firstly, the basement walls' color was black / dark gray and we discussed on the phone that they will use some neutral color for it.

If that is the case I like my house to flow throughout, so I would use the same flooring and color you use in the other main areas of the house.

My very first meeting with lenders, I had mapped various sample financial deals (one for each lender) from the biggerpocket.com calculator, printed them in pdf color and showed the lender that I had an understanding/command of certain business terms (cash on cash, IRR, ...etc). 

It's a condo built in the 70s that needs some framing, drywall work, flooring, cabinets hung, bathroom surround tiled, electrical outlets replaced (because it's dumb when they're all different colors), & doors hung.

I personally like the tile you have pictured but something with a bit of color could work too

I wouldn't blame the tenant but what I would do is paint the mailbox (and the post holding it up) a random color so if somebody hits it and the paint rubs off it will be easier to figure out who is at fault (as the paint will likely rub on the car that ran into it). 

So I went with a darker color.

Remember, the FEDERAL Protected Classes are Race, Color, Religion, National Origin, Sex, Disability, and Familial Status. https://tinyurl.com/y9acgrtsStates, Cities and Municipalities MAY ADD to the list of protected classes.

For example specified by region and sun exposure so paint colors are relevant to the space.

Sure you can paint a wall, just run the color past me so I know I can paint over it easily if you leave.