Afterwards, I painted on a very thin layer of Iyanden Darksun 1:1 mix going against the raised edges of the armor. This part wasn't important of making sure that the recess was darker, but to ensure that I had an even coat throughout the miniature. This would be for a much more reasonable base color for the next yellow to be painted over without having to clump on layers upon layers of paint.
The next step was to paint the model using Sunburst Yellow, making sure to paint carefully around the edges of armor plates and recess areas allowing the darker colors to show a bit. At first I wasn't too sure about this because the overall model came out so bright. I knew that I was going to give the marine a wash of some darker paints, but just wasn't sure of myself.
Instead of washing the model with a GW wash or a very diluted paint to water mixture, I tried something different. I had recently purchased the weathering powder from Forge World and wanted to give it a shot. I put some Orange Rust on the edges and recesses of the marine (not too heavy, just a dab here and there). I took a clean brush, dipped it in some water and then started to feather the water into the powder. I feathered the water:powder mixture towards the middle of the armor plates and let it sit to dry.
Once the model was dry, the bright yellow marine had turned into a more rich yellow. With weathering in the recesses. The perfect yellow for my taste when painting Imperial Fists, or other yellow stuff :P I havn't finished the model yet, but once I finish the entire model/squad, I will post it up for all to see.
Hope this tip helps anyone who gives it a try!