My boy is 5 months and eating solids... Should his pops be hard? And what colour is not right and what's normal?

Stool will harden. As babies transition to solid foods, their stooling patterns and consistency and colors will change. It is normal for the stool to get hard, but you do not want it to get hard to the point of constipation. Increasing fluid intake can help. The only colors i concerned about are white, black and tarry, and stool with bright red blood mixed with it. Everything else is ok (yellow, green, brown, etc.).
See below. 5 months is early for solid foods. Use age-appropriate baby food and his stools should normalize.