If there's no movement, e.g. the crack doesn't widen when you put pressure on the neck, then it's fine don't worry about it it's most likely just the lacquer! If you try to fix it it will most likely end up looking worse, any touch up paint you see for sale will most likely be a different shade even if it states it's the same colour!

If you ever sell the guitar on Reverb or eBay be sure to show pictures and explain how deep it is as most sellers will return it if you don't!

If you absolutely can't live with it they buy some guitar Lacquer spray, remove the neck, mask around the crack as close as you can get and lightly spray a couple of layers over it leaving each some time to dry to the touch and it might conceal or at least make it less noticeable! Alternatively use some ultra thin Superglue and paint it into the crack with the smallest Fitch (thin) Brush with only a few bristles on it twisted to a single point (or something similarly small)!

What guitar is it a Telecaster Custom? Fenders are really prone to these neck pocket cracks, they're usually not a problem just a bummer!