Changing text colour midway through a sentence with expressions

I am trying to create a MoGrt for a client, and at one stage the client needs to input 2 values in the same text sentence, the issue I'm having is I need the second input to be a different colour.

My source text field will look something like this:

"input 1" + (different colour)"input 2"

I cannot seem to find the right way to word this in expressions, to change colour at the marked point. I know how to link the text input using other text layers but can anyone help me with the expression to change the text fill colour before the second input.

Thanks!