  It is widely recognized that the irregular satellites of the giant planets
were captured from initially heliocentric orbits. However, the mechanism of
capture and the source region from which they were captured both remain
unknown. We present an optical color survey of 43 irregular satellites of the
outer planets conducted using the LRIS camera on the 10-meter telescope at the
Keck Observatory in Hawaii. The measured colors are compared to other planetary
bodies in search for similarities and differences that may reflect upon the
origin of the satellites. We find that ultrared matter (with color index B-R
$\ge$ 1.6), while abundant in the Kuiper belt and Centaur populations, is
depleted from the irregular satellites. We also use repeated determinations of
the absolute magnitudes to make a statistical estimate of the average shape of
the irregular satellites. The data provide no evidence that the satellites and
the main-belt asteroids are differently shaped, consistent with collisions as
the major agent shaping both.
