If you want to change the pH of the solution, you could add hydrochloric acid dropwise until it reaches the particular pH/color you're after. I'm with hoppy though, my indicator solution comes out of the bottle on the yellowish side.
The buffering capacity of the few mL of 4 KH solution in the drop checker should overwhelm the pH of a couple of drops as long as the drops are fairly close to neutral (i.e. greenish.) When you add the drops to the drop checker, it will turn blue because of the bicarbonate that you've put in there.
When you wrote that you injected CO2 into the solution and it didn't change color, did you mean that you injected directly into your indicator, or that you prepared a 4 KH buffer, put drops in, injected CO2 for a while, and nothing happened? If it was the first, I'm not terribly surprised, as it sounds like you made it fairly basic. If it was the second, could you have made an error in your buffer solution?