sld - Styling WMS layers in OL3

I have managed to get my WMS layers working in OL3.
Now I want to style them, as they are all set as blue on the server side and I can't change that. I know the common answer seems to be WMS is an image and you can't style it like a vector but there are examples of people doing complicated dynamic styling with SLDs so it must be possible to use an SLD to change the layer colour - depending on the server?

I have had a look at one examplebut that is OL2.9 and for WMS.post layers and I don't know what they are.

My rough ol3 code is here so you can see where I am at