Exterior Paint

This is the back that I will need to power wash. But I need to add some color around the trim.

I think you are on the right track. Found an inspiration pic that might work for you:

Design 2 - Heathcote Road · More Info

PS: don't power wash the brick. Clean it.

I don't know and the insp pic didn't have suggestions either. Maybe one of the color experts can pop in and give you a couple of suggestions. You might have to try to sample anyway so the gray you choose works with your specific brick.

Here is one that is darker that looks stunning IMO https://www.pinterest.com/pin/319403798552891077/

Here is another one with a dark gray (soft black) like you suggested originally. Two views shown below.

^ The trim is F&B "Railings" color. F&B refer to it as a soft black

http://us.farrow-ball.com/railings/paint-colours/farrow-ball/fcp-product/100031