What's expiring vs current

Hello and welcome to the forum.

This will require 3 conditional formatting formulas (one for each color).

Let's say that the license expiration days are in column A starting in A2. Apply the following rules in this order:

Green
Highlight A2:A100 (or however far your data goes) > Conditional Formatting > New Rule > Use a formula
=A2-TODAY()>=90
Format: Fill green > OK > OK

Yellow
Highlight A2:A100 (or however far your data goes) > Conditional Formatting > New Rule > Use a formula
=A2-TODAY()<90
Format: Fill yellow > OK > OK

Red
Highlight A2:A100 (or however far your data goes) > Conditional Formatting > New Rule > Use a formula
=TODAY()>A2
Format: Fill red > OK > OK

If there can be blank cells in the column, you can use this as the red formula:
=AND(TODAY()>A2,A2<>"")

and this for yellow:
=AND(A2-TODAY()<90,A2<>"")