To help learn, I decided to paint my wall in Photoshop. I created a selection with the pen tool, new layer mask, new adjustment layer. I can use Hue/Saturation and change the colors. But what I can't do is match a paint color exactly. For example, if I have this hex value, #6C6A66, how do I get the wall that color? If I do a color fill layer, it looks horrible, because well, it's a fill layer, not an adjustment.
There's a Photo Filter Adjustment Layer where you can put an Hex Color Number (at the middle of the image).
But is a Photo Filter, that depends on the result to get. I think a Color Fill Adjustment Layer with Color Blend is a good solution (At the left).
A good trick could be duplicating the Photo Filter Adjustment Layer (the central block of the image), the result is much refined than the Color Fill Layer:
I'd encourage you to use Curves Adjustment. The issue being control. If you have a wall it isn't one color, it's got tones created by texture, paint inconsistencies, and light/shadows. A Curves Adjustment is a better approach for this because you're going to have to specify what point you want to be exactly #6C6A66 --- probably a midpoint.
I used Odette by Jean-Philippe Delberghe on Unsplash for this example. I didn't spend much time on the mask so its a little rough but you get the idea. Where the Info Point is placed is exactly #6C6A66 with the curves adjustment turned on.