Guess the Pattern

[True Federalist (진정한 연방 주의자)]

I have two patterns and since I've already got it mapped I'll go ahead and post it

[True Federalist (진정한 연방 주의자)]

Ernest-population based, I presume. Maybe red are states with EVs rounded up, Blue are rounded down, and grey are given what they have only because it's the law?

It does have something to do with EV's but nothing to do with rounding.  Your grey observation isn't quite on target either, as Vermont is red yet it had less population than Alaska in 2000.

[True Federalist (진정한 연방 주의자)]

It’s been long enough that I’m going to go ahead and give the answer.

Red means that the last time the state had a change in EV’s it lost electoral votes.
Blue means that it most recently gained.
Grey means that it never had anything other than 3.

[True Federalist (진정한 연방 주의자)]

When did Delaware have more than 3?

Delaware had two Representatives and hence 4 EV's as a result of the 1810 census.  The 1820 census brought the State back down to 1 Representative where it has been ever since.  So a 4 EV Delaware existed only for the 1812, 1816, and 1820 elections.

[True Federalist (진정한 연방 주의자)]

Here's a new pattern:

As a hint, the choice of green instead of grey was deliberate for this political map.