The Arvada Center’s “In Sight On Site: Murals” is a big, juicy piece of late-summer bubble gum, a bang-up, heat-beater of an art show where the chewy thrills come in bright colors and eye-popping patterns. But, honestly, it left me with an uneasy feeling. In the way that candy ultimately disappoints, the fruity flavor ran out quickly, and I found myself looking for a way to dispose of something that didn’t taste quite right. The exhibit, with 21, large-scale murals by several of the region’s most respected artists, is an experiment of sorts, taking our current fascination with outdoor murals, which appear relentlessly in urban zones these days, and moving it inside.