Red and green, blue and orange
The contrast of Red and Green side by side will cause retinal fatigue. Here is a source of some very interesting information on color: http://webexhibits.org/colorart/simultaneous.html
foreground
The color in contrast to red is green.
No. Red and Yellow are both primary colors. A primary color needs a secondary color to contrast with it. The contrast to red is green and the contrast to yellow is violet (purple).
The color of the rainbow with the highest frequency is violet.
You can create an intensity contrast in your artwork by placing a pure, bright color within areas of grayer, low-intensity color. The neutral nature of the gray color will provide a striking contrast for the pure hue.
Text
Brown
Purple or lavender would be a good contrast color for lemon yellow, as they are opposite on the color wheel and create a bold and vibrant visual impact. Additionally, navy blue or gray can also create a sophisticated and elegant contrast with lemon yellow.
White can be a bold color choice, provided it has contrast.
They are called complementary colors because they complement each other with the highest intensity.
Contrast.