In the last decade or so, dinosaurs have started being depicted as brightly colored. The reason for the trend of brightly colored dinosaurs in movies is that in recent years techniques for identifying pigments from fossils have been developed, using electron microscopy and ion bombardment mass spectrometry.
News report: Ancient Pigments Unearthed: Fossilized skin reveals the colors of three extinct marine reptiles by Ed Yong. The Scientist, January 8, 2014
Original article: (Abstract) Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles. Lindgren et. al., Nature 08 Jan 2014
and news report: Pictures: Dinosaur True Colors Revealed by Feather Find, Chris Sloan, National Geographic Daily News
Original article: Zhang et. al., 2010
Fossil color studies were pioneered by Jakob Vinther at Yale
No doubt movie speculation is running far ahead of the science, but these are the discoveries that unleashed the trend of brightly colored dinosaurs. At this point, it is reasonable to think dinosaurs are as brightly colored as birds or reptiles are today, and in some cases the coloring of specific species is known.