So I started to work a tad on this common lighting practice scene, but before I got too far, I ran into a problem. I couldn’t find a way to control the color of the specular highlingts. For example, the highlights on the banana should be white, but they are yellow.
Are you sure they should be white? I mean, I have a banana on my counter and it doesn’t seem white, rather a brighter yellow/green. I know the plastics and glass might have more white spec, but not so sure about fruit. Maybe if you mix a glossy bsdf with a diffuse you might be able to get one by reflecting a white emitter…
Hmm, true I guess a banana is not a good example. However, i did run into this problem with wood as well, which does have white highlights sometimes.
Perhaps with the wood, you are really talking about the polish or polyurethane coating - in this sense, maybe you can adapt some of the techniques used in the car material thread.
Fresnel--------------fac
Diffuse--------- Mix--------
Glossy----------
Glossy controls the highlight colour. Hope that makes sense. 
Artales means something like this:
NB: The lamp is an area lamp type with default values. It emits a pure white color. As you can seen, the glossy shader controls the specularity.
Ya that’s it. Sorry I was ‘sans’ 'puter.
seems to me that as you increase the fresnel effect, you also lose the diffuse color a bit. You need to balance the fresnel effect with adequate lighting, and by increasing the power of your lamp/emmision source, you get a stronger white. I wonder about some kind of math node for tightening the highlight for plastics.
You can use math nodes or the bright/contrast node to modify and tighten the fresnal gradient to the point where there’s almost no transition between solid diffuse and solid glossy.
Do note though that you will need a color mix to clamp the values of the mixing data between 0 and 1 before plugging it in as the fac. otherwise you might be mixing with a much higher range of values and getting a wildly incorrect result.
