Hm, I have not yet experimented with mixing normal paint and foundation paints, so I can't comment on your ideas.
Fast version: What you can do is apply Devlan Mud to the entire clothing (perhaps thinned down a bit). That will darken the clothing, especially the yellow. You can then highlight with the initial colour. Personally, I don't like the look on my minis, but some members here use the washes to great effect. Look for Zero_Zwentythree and Shadowlord.
Slow version: For sharp highlights on red, I recommend mixing it with Elf Flesh instead of lighter reds, using pure Elf Flesh for the final highlights. Conversely, I find Dark Flesh is good base colour for red if you are layering it.
Edit: You're welcome! I recommend browsing around a bit here, there are some great painters on this site.