I'm replacing my factory horns with louder aftermarket ones. I just need to know which color wire is positive and negative at the horn connectors.

 

do you have access to a test light or DVOM? the easiest way would be to use a test light and have someone hit the horn. which ever wire causes the light to illuminate when the button is pushed will be your positive.

 

Did a quick search and I can't find the schematic for your car,
However, through several years and generations, Honda uses the Blue/red wire as positive.