I knocked my hand against a phone slightly and 2 hours later I developed a green vein coloured patch 3cm by 1cm. Causes? Its also has a dull ache.

Bruise. You've likely bruised your hand, which causes discoloration and pain. It will take about 7-14 days to resolve. If you should have increased pain, constant numbness, tingling, or weakness get checked right away though. Occasional episodes of brief tingling is usually normal.