The essence of creative cooking is improvisation. Sometimes that improvisation is a response to a lack of ingredients. Don't have whole milk? Mix cream and skim. Don't have shrimp? Try the recipe with scallops. Necessity has created many an inventive dish from the materials at hand.
And then there are the dishes you make just because you think they sound cool. A year or so ago, we had guests over where every single item on the menu was purple. (I did mention my wife is a patient woman, right?) We started with a leek-potato soup made with Peruvian blue potatoes, moved on to a red onion tart which turns purplish in the oven, and had on hand purple drunken goats cheese. The rind is stained a deep purple by soaking the cheese in crushed wine grapes.
The picture you see (and which you can click to open a larger version) are some of the star ingredients in a dish I wished I'd had at that meal. I took the pesto recipe I posted a week or so ago and substituted these gorgeous purple basil leaves I bought at the Chicago Green CIty Market, and some walnuts, while upping the proportion of nuts to leaves and decreasing the cheese somewhat. The result is a bitter but delicious basil-walnut pesto with a deep dark purple coloring.
I might increase the oil over the original recipe and use walnut oil instead of olive oil next time. I might include some blue cheese as well. Or I might not. I might try tarragon instead of basil or any of a thousand variations.
You get the idea. Experiment. You might very well create something disgusting (in which case, give it to the dog and call for Chinese), but you might also make something new and wonderful. As you experiment you'll figure out how a dish "works" and what you can vary and what you can't.
One caution - this doesn't work so well with baked goods. Freaky magical chemical reactions happen in the oven, involving stuff like glutens and disaccharides and elves. Yes, elves. I haven't seen them, but I know they're there. So expect to be disappointed if you do much more than tinker around the edges of a successful baked goods recipe until you figure out what makes a cake (for instance) do that fluffy lovely thing it does. That doesn't mean you shouldn't try, but you should be more ready for the laws of chemistry and physics to hate on you. (Why you gotta be a baker-hater?)