Question: what to do when you have no white paint?
Answer: Squeeze a pea-sized amount of acrylic paint onto your palette that you want to lighten. ... 
Squeeze a pea-sized amount of yellow near the first color you squeezed. ... 
Dip the brush into the yellow again. ... 
Squeeze out an oil paint color onto another palette. ... 
Mix the yellow with the original oil paint you squeezed out.