I like the color scheme.
I agree with the others about yellow. I have been airbrushing a long time but still have problems with yellow. I found out, the more red the paint has, like the UP yellow, TTX, the easier it is.
On your paint scheme, I would move the green/yellow separation more to the left until the upper corner touches the cab. It will give you more room for the lettering and you don't have to mask over the uneven surface of the grill.
I also would think about yellow paint at the flat surface at the rear end.
About the lettering. If you do them in yellow, you need to match the paint with the rest but not with white but white could stick out too much.
Not an easy choice to make. Maybe yellow or white with black outline could also be a choice.