Here's a question from a fellow designer.
"What do you do when someone wants you to use colors you hate in a design? I've had this happen before (bright green and yellow!), and the client loved it, but me, not so much. :/"
There's a few things I go through in this situation:
1. I ask myself if hating the color is a personal preference. For example, my childhood bedroom was painted light ice yellow, and I really can't stand that color these days – but that's my problem. If so, then I try, try, try to overcome it. In most cases, the design winds up looking pretty good if I manage to get over it.
2. Or, maybe I hate the color in combination with the other colors in the brand or the website. The hated color could clash with them, or they could just look awful together. Some colors actually make each other look muddy or too bright just by sitting next to each other – they each reflect the others' color properties, and wind up looking totally different (and in some cases, just bad!). If this is the case, I'll see if there's a neighboring color that looks better – for example, if the offending color is an olive green, a deep kelly green might look better.
3. The color could be a bad match psychologically for the brand. Say, for example, a company is trying to communicate "cutting-edge" with their logo, and they want their colors to be navy and slate grey. There's not a lot that's cutting-edge about those particular colors. In this case, I would propose more appropriate colors, but make your case to the client. Tell them about what the various colors mean, what you're trying to communicate with the brand/ design/ piece, and then explain how your newly-proposed colors communicate that message.
Look here for some pretty good psychological definitions: http://en.wikipedia.org/wiki/Color_psychology
4. The colors might not have enough contrast to make the design legible. For example, in your yellow and green example, if it's a bright yellow and lime green making up a logo, then there may not be enough of a difference between the two colors to distinguish the various parts of the logo from one another. Or, you might find yourself in a case where the client wants a very light-colored text on a white background – which makes reading very, very hard. Or, they may even want white text on a dark background – which is fine for short bits of text (like a tag line), but very hard on the eyes for paragraph reading.
If this is the case, again, explain to the client why it's not a good idea. Show them your recommendation. Explain things in terms of design and communications effectiveness.
5. You might just have a client who wants to see their favorite colors on their designs. This happens a lot in the case of small businesses – the entrepreneur running the business may just really love those colors. Many entrepreneurs forget (or just have never been told) that the job of their designs for their business is to communicate with and entice their target audience.
If this is the case, explain to them that your job is to find colors with the right message, and to find colors that the business's prospects and target customers will like. They can have a car, wardrobe, and home furnishings that are all their favorite colors – but their logo needs to be designed in their customers' favorite colors in order to be effective.
I hope this helps!