Using a limited number of colors does help give unity to a painting. Even if a painting is well painted and the technique is flawless, without a sense of unity, the picture will lack the 'viewer's holding power.'
It's a strange thing that if a painting has unity, you don't think about it being there, but when it doesn't have it, you get that feeling that 'all-is-not-right-in-this-painting. Fortunately, a limited palette is only one of the ways to help create unity.
Most of my paintings have between eight and fourteen colors. I started out in watercolor by selecting two reds, two yellows, two blues, payne's gray, and burnt sienna and have gone through a lot of paint since then.
FYI - my favorite, can't-live-without-them colors include Hansa Yellow, Permanent Yellow Deep, Raw Sienna, Quinacridone Burnt Orange, Quin Coral, Transparent Pyrrol Orange, Perlene Red, Quin Magenta, Cobalt Violet Deep, Cobalt Blue, Indanthrone Blue, Ultramarine Turquoise, Cobalt Teal Blue, and Green Gold, with the italicized ones being my top eight. All are Daniel Smith brand watercolors, a company in Seattle, Washington, and first seven are cool colors, the last seven are warm. I'd toss in Lunar Earth, Quin Violet, Serpentine, Perylene Green, Phthalo Blue, Cerulean, and Lunar Blue if I could have twenty one, although I doubt I would ever actually use that many in one painting.
This weekend, I'll be watching sailboats on beautiful Klinger Lake in Michigan where fellow artist and friend, Lynne Kasey, is opening her beautiful lake front home for a very unique art show. It will be a great weekend, and I'm really looking forward to it.
I'll be back to the blog after the show. See you Monday.