If white light is made up of all colors, how can you tell what color an object is.

See explanation

Step-by-step explanation:

White light is composed of seven different wavelengths. This can easily be established by using a prism to separate the various wavelengths that constitute white light.

How come we get to tell if an object has a particular colour? We get to know colours because the observed colour of an object is the wavelength that is reflected by that object.

An object that absorbs all other wavelengths in the spectrum of white light but reflects red light will appear red to the eye.