Images + color

I recall seeing (somewhere) a tip on how to modify black + white images (using Photoshop???) that can be used with a color overlay … like the handful that comes OTB with Blocs?

Can anyone direct me to where that is posted, or how to do so?

Thanks!

Perhaps a better way of phrasing this is modifying the opacity of images. Pretty sure I spotted this in the forum some time ago.