First let me say if you have not done this type of work get a professional to do it, or at the very least review your plan/work before connecting the circuit.
Do you know if the SWG is 120V or 240V? If it is 240 colors will be the exact same as your pump and I believe by code has to be on a separate breaker , if it is 120V which I think most SWGs are would be black green white, white being neutral. If your equipment is all 240 you may not have a neutral at your sub panel and if that is the case you will have to pull a white stranded 12 awg THWN from the main panel. You can't go wrong with 12awg but may be over kill for the SWG you want stranded THWN the W stands for wet locations The manual should tell you the draw and once you know that you can look up what the minimum gauge to use I suspect 14awg will work but let the manual tell you for sure.