Professor Oak

Hello my fellow tree enthusiasts! I’ve been growing an oak sapling for several months and its leaves are discolored and I’m not sure what the cause is. I think it gets enough water, light and nutrients. Would appreciate some advice if someone can spare some! P.s. where I live a certain bird often hides many acorns all over the city but forgets where they have stored them. Then on rooftops and balconies little oak saplings start growing from plant pots and containers. This sapling comes from such an acorn :)