Honestly, from the looks of your models, I don't think that you need to change your method with washes. Washes will typically darken a model, so it's good to think two or three colors ahead of the layer you're on. This is not always the case, but is the majority of the time. Also, a red wash on red paint won't show up at all. Browns won't do very much to red either, though it does change it slightly. Just maybe not enough to notice on the table top when you have hundreds of models out. Nuln Oil will work well with red, just apply it lightly, building up to the point you want (Be careful with pooling) and then be ready to highlight and drybrush with a lighter shade of red.
You obviously haven't finished your Skink Priest in the photo you posted, but for example, from the pic, I would apply a wash of Nuln Oil to the gold portion of his staff, then after that dries, I'd apply a highlight of the same gold color, then a drybrush of a much lighter gold color. That will allow it to layer appropriately and really achieve a nice depth. Personally, I like this method, though on that model, I also like a little more color on the gold portion of his staff as well, since the rest of the model has so much variation in color. One monotone color kinda distracts from the rest of the model. (You were probably going to do that anyway, but I've just seen way to many people do that with this model.

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Hope that helps!