I think it is still a red county. Throw out the college dead weight and it would be even redder.
Throwing out ultra-liberal colleges would be great, but is probably not a viable option. If Denton County is still "red" at all, it is the palest possible shade of pink.
Whites will be a minority in Denton any minute now if they aren't already. This county which once gave astronomical margins to Reagan and Bush is barely a 55% R county now -- and decreasing.
Demographics and Election Results from Denton County, TX
As can be seen here, the 2020 precinct-level election map shows that the area around Denton and the southeastern part of the county are already pretty bad.
Collin County, also formerly quite nice, is even worse than Denton. There's a non-insignificant chance that it will vote red -- commie pinko red -- in November.