The link (as of mid-May 2015) mentions that "Francis was initially influenced by the work of abstract expressionists such as Mark Rothko, Arshile Gorky and Clyfford Still. He later became loosely associated with a second generation of abstract expressionists, including Joan Mitchell and Helen Frankenthaler, who were increasingly interested in the expressive use of color."
That influence must have been indirect, because Francis apparently did not spend much time in New York City, the hotbed of Abstract Expressionism and other modernist abstract painting schools. I suggest that he was also influenced by Jackson Pollock of drip painting fame. A photo (below) shows Francis in his studio with paint pots and canvases covering the floor Pollock-style.
Whereas Francis' paintings often featured drips of paint and running paints, they often didn't have the entire surface covered, as was Pollock's classical case. Segments of paintings were left blank, with the result that the images appeared to have greater structure than the typical Pollock wall-to-wall swirls of drip. The white backgrounds Francis used also served to highlight his selection of colors -- typically bright and cheerful.
I rate Sam Francis as an interesting footnote to an artistic school whose time has long passed and whose goals make far less sense now than they did when new.
Sorry, but I don't have a source for this photo.