Hungry - hungrier - the hungriest

Difficult - more difficult - the most difficult

Big - bigger - the biggest

Dark - darker - the darkest

Yellow - yellower или more yellow (зависит от подтекста) - the yellowest или the most yellow (тоже зависит от подтекста)

Young - younger - the youngest

Old - older - the oldest

Long - longer - the longest

Foggy - foggier - the foggiest (точно не знаю)

Tall - taller - the tallest