OpenGL GLSL - Text rendering query

[LP]

I thought by having the font in white I could colorise it using glColor prior to my glBegin(GL_QUAD) glVertex..... etc. that binds the glyph in the font texture to the four vertices. Unfortunately this changes the color of the fill behind it, so as I understand it, I need to use shaders to achieve what I want but I'm struggling.

Try calling the following before your rendering loop:

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

DON'T.
I beg you, stop and rethink your strategy.
Any code that has glBegin/glVertex/etc. in it will be doomed to the compatibility ghetto, limited to 20k vertices while any semi-modern hardware is capable of millions.

This is a really bad advice. See this: Nvidia: Deprecation Myths. Of course everything pre-GL3 is considered legacy now, but it doesn't mean you can't use it for learning. Newer APIs such as Metal/Vulkan/Direct3D 12 are notoriously difficult to get started, so if you want to get something working quickly, glBegin/glEnd is as good as any other option, and in regards in performance, it is likely faster than the source code you suggested (and I challenge you to prove different: do the benchmarks!)

I would suggest to use whatever technique you find easier to learn - it is better to have something working in the way you want, than not having anything at all.