What is the best way to search for a pixel in a screenshot?

[scidam]

I would recommend the follwoing approach instead of using loops directly:

# image.shape = (height, width, colors)
# pixel = np.array([R, G, B]), i.e.numpy array of length <the number of colors>
# threshold -- scalar value, takes into account color similarity 
np.where((np.abs(pixel - image) < threshold).all(axis=-1))