Except under the best of conditions, it is hard to see feather colors accurately. Light reflection and shadows often distort, dull, or exaggerate colors. Consider other factors first. If conditions are good, consider color a bonus. Of course, there are species for which accurate color determination is essential for accurate identification.
Size is usually helpful, but conditions can be misleading.
A bird soaring overhead or flying by may seem much larger or smaller than it really is. A reference object is helpful - a tree, fence post, telephone pole, etc. Observe the shape or profile of the bird. A long-bill, long legs, or tufted head immediately eliminates many possibilities. Habitat is always a useful consideration.