red is better during the day cause altho amber travels further in more conditions, people are more cautious about red

1) they see red clearer during the day (esspecially LED red)
2) red in fog can be seen (although not as well as amber) but at further distances people will tend to slow down and take caution cause they think "it could be a cop" I'd stick with red led.

you could always use a circuit to chage to amber when you have your foglights on too. (or even easier a 3 position switch on the dash)