Multiplication is one of the most common ways to blend colors in a shader, but there's really no limit to how you can combine color values. Try experimenting with different algorithms in the fragment shader to see what effect it has on the output. What happens when you add values instead of multiply? What if you use the red channel from one texture and the blue and green from the other? Try out the following algorithm and see what the result is:

fragColor = vec4(texture(uSampler2, vTextureCoords).rgb - texture(uSampler, vTextureCoords).rgb, 1.0);