Nice to see you back in action

As for your problem. While I can't provide you any code since I don't have enough experience with OpenGL I can tell you that there are generally two approaches to achieve what you desire.
  1. In first you simply draw your colored square on quad using your text texture as alpha mask so only text portions is actually rendered. As far as I know this doesn't require use of shaders. This should work just fine with your example images since your font image is just black and white.
  2. In second approach you would use simple blender shader which uses alpha channel of your font texture to actually determine the render area. This shader would then render your font texture and blend it with desired color. And as far as I know when using shaders you don't need to provide your desired color from another texture but you could even pass it to shader as an input parameter.