Objects appear to be different colours because they absorb different amounts of the red, green and blue light, and reflect the rest of the wavelengths in visible light. White objects reflect all light, black objects absorb all light. Red objects reflect red light whilst absorbing green and blue light.
Scientists use different substances/ chemicals to absorb different amounts of the red, green and blue light in white light to make things different colours, eg. some chemicals dye things yellow (a combination of reflected red and green light) whilst other chemicals might absorb all the red light but reflect equal quantities of green and blue light to make cyan.
