When it comes to color reds can really draw a viewers attention. A red rose on a green background is a great combination because reds and greens are contrasting colors which are typically pleasing combinations. You can pick contrasting colors by using a color wheel. The contrasting color will be on the opposite side of the wheel, such as red-green or blue-orange.
I was recently out shooting at a local park after one of our more significant snow storms and came across a few subjects that really show the power of red in a composition
|Red Bench at Lake|
|Red Bench Under a Tree|
|Toyota Tundra in Snow|
In each photo it's easy to see what the subject is and our eyes are drawn right to it. In fact, it's hard to look at anything else in these photos. The red is more powerful because of the lack of other color in the winter scenes.
Of course red can work against you as well. If your subject is a more subdued color and there is a red object in your composition your viewers attention will be drawn to the red objects, even if that's not where you want them to look.
Next time you are out shooting look around and be aware of colors. Use them to your advantage to create a more powerful photograph.