When you want to colour something, it is easy start by reducing all existing colour info to greyscale, while still staying RGB mode to keep the three channels available.
This can easily be done by setting saturation (Image>Adjustments>Hue/Sat, or Ctrl/CMD+U) to minimum, although I prefer the monochrome option down left on the Channel Mixer (Image>Adjustments>CM) because it gives me the option to use the three sliders of the three channels. Much can be enhanced here.
Then, when it comes to colouring, you can indeed paint on a new layer that is set to color blend mode. But there are times when you just want something else.
One option is to posterise the image and then select a certain hue and fill it with a colour of your fancy. In case we're talking about say, bevelled fonts, this selecting can be tricky.
Yet, if you add some pixels to the bottom of the file (Image>Canvas size) and drag a gradient with the default black and white, this will posterize with the image. And here, all your hues are easily selectable.
Just don't forget to set the magick wand's sensitivity to 1 and to uncheck the contiguous option. I also start with an unsharp mask.
Filling with the foreground colour can be achieved with pressing Alt+Del.
As we only fill one hue at the time, more is not necessary.
The example is very restrained, but you can go way into the realm of dayglo and psychodelirium.
Oh, another advantage: afterwards you want to change a hue. Just take your magick wand, click on the hue of your fancy in the posterized gradient and done.
This can easily be done by setting saturation (Image>Adjustments>Hue/Sat, or Ctrl/CMD+U) to minimum, although I prefer the monochrome option down left on the Channel Mixer (Image>Adjustments>CM) because it gives me the option to use the three sliders of the three channels. Much can be enhanced here.
Then, when it comes to colouring, you can indeed paint on a new layer that is set to color blend mode. But there are times when you just want something else.
One option is to posterise the image and then select a certain hue and fill it with a colour of your fancy. In case we're talking about say, bevelled fonts, this selecting can be tricky.
Yet, if you add some pixels to the bottom of the file (Image>Canvas size) and drag a gradient with the default black and white, this will posterize with the image. And here, all your hues are easily selectable.
Just don't forget to set the magick wand's sensitivity to 1 and to uncheck the contiguous option. I also start with an unsharp mask.
Filling with the foreground colour can be achieved with pressing Alt+Del.
As we only fill one hue at the time, more is not necessary.
The example is very restrained, but you can go way into the realm of dayglo and psychodelirium.
Oh, another advantage: afterwards you want to change a hue. Just take your magick wand, click on the hue of your fancy in the posterized gradient and done.
I shall take some time to experiment with same!