Yes Frank. Just a bit more than one colour in your base layer. Maybe a touch of yellow ochre or gold oxide. Looks like you base is red oxide so maybe some burnt sienna as well. And even a touch of blue. You don't need distinct transitions in the under colour, just a mish mash blend. I think it would make the brick wall come alive.
I expect you plan some dry brushing over the top of what you have done. Don't forget a tiny bit of sulphur yellow here and there. It's industry after all.
I possibly go a bit over the top on colour for most folks. But the unexpected colours are there in the real thing when you look hard enough. And I very rarely use black. Certainly not straight black. Its usually either very dark blue, green, purple or brown.