Looks like you have plenty of advice on places to buy.

As to color, I'd stay away from white, but that's a personal matter. I only wear white with black tie (PC) or formal, and some people don't even like white in those situations. (Problem is, I ordered a custom knitted pair in white years ago, so I wear 'em when I deem them appropriate.)

If I were starting over like you, I'd go for either Lovat Green or black or novy blue. Since you're wearing khaki shirts, I assume this is not a formal affair. (You can see my picture with the color combination:


This is kind of the combination that the Highland Regiments wear, or at least used to wear. Who knows what they're up to since amalgamation.