One of the best skills a designer can learn is how to talk to the left-brain types. What is important to them? That is how you should frame every point you make. Here is a list of left-brain values:
the bottom line
The key bridge word is “communication.”
Take your right-brain stuff and use their words to reframe the issue. For instance: they want to use puke-pink on their website for men’s sports:
Say, “This design will be more effective, and communicate better to the target audience if we use this blue that has statistically been shown to appeal to men of our target age range. My research has shown that when men see this color, they buy products. I have even tested various shades of the blue to determine which shade delivers the maximum PPC, sales, click through…”
You could veer towards the silly with this, and have to be careful not to be sarcastic. You have to have solid proof that they will accept. The LB (left-brains) are very insecure with the RB’s way of doing things (by the seat of our pants — pure instinct), so you have to make them feel secure by using safe-sounding LB words.