What is an indication that grass needs to be fertilized?

Pale coloration in grass is indeed a key indicator that it may need fertilization. Grass that lacks adequate nutrients, particularly nitrogen, often displays a yellowish or pale appearance. This is because chlorophyll, which gives grass its green color, requires sufficient nutrients for production. When the grass is not thriving due to nutrient deficiency, it struggles to maintain its vibrant green color.

While thick growth can indicate healthy grass that might not require additional nutrients, and an increased weed population can point to various issues including competition for nutrients, the specific symptom of pale coloration directly suggests a nutrient deficiency that might be addressed by fertilization. Therefore, in the context of this question, pale coloration is the most straightforward indication of the need for fertilization.