78 is the underside colour for desert birds and will be too blue. Lighten with white and light gray like you say and it should work.
If you're going to pick one of those two schemes on the box, you're kind of already commited. The one on the right is a Jabo of KG51 and it would have dispensed with two of the cannons in the nose. You've taken pains to put all 4 in already. The one on the left is Yellow 8, W.Nr. 112385 of JG7. The yellow band on the fuselage is bogus - should be a blue and red band. It was finished in an overall 81/82 scheme on the uppers (brownish green and medium green respectively).
Here's a better profile: