Is it best to use two or three colors on exterior of house?

One for the house, one for the trim, one for an accent.

I'm in the process of choosing paint, and many sites say 3 colours.

I for one, prefer to paint my eavestroughs the same colour as my siding, so it isn't a focal point, but many choose a colour for the siding (brick colour counts), a 2nd colour for trim, and a 3rd for doors and/or shutters.

http://www.prattandlambert.com/color-and-inspiration/color-collections/exterior/light/

https://www.sherwin-williams.com/CategoryDisplay?parent_category_rn2=21202&urlRequestType=Base&catalogId=11051&categoryId=21208&urlLangId=&beginIndex=0&langId=-1&top_category=&parent_category_rn=21199&storeId=10151

https://www.benjaminmoore.com/en-ca/project-ideas-inspiration/exteriors/home-exterior-ideas-inspiration

http://www.behr.com/consumer_ca/inspiration/exterior

i would case the neighborhood...which do you see more of? What colors are used...is it an historic neighborood? If so there could be historical references ...

my house has vynial siding. :c

Depends on the architecture of the house. Generally speaking, the more modern the building, the simpler the paint job. Many homeowners of houses built in the second half of the last century go monochromatic white. A Victorian, on the other hand, with all its attendant filigree and trim detail could easily handle 3 colors, either a monochromatic display of 3 shades of one color, or three different complementary colors. Examples of each can be found in every city across the land.