Youtube account CardShuffler99, who has over 189,000 subscribers on Youtube, has broken down the skill behind several of Eric Chien’s acts.
Before explaining the magic tricks Chien used in his audition, they preface their “reveal” by saying there’s no proof that their ideas about Chien’s magic tricks are actually what he’s executing, and that everything in the debunking video are just theories. The complete 10-minute explanation video is viewable above.
To explain the color-changing cards, CardShuffler99 suggests that the top half of Chien’s deck (the part he reveals to the audience) is red cards, while the bottom half is a hidden stack of blue cards. By doing deals and bottom deals on either side of the table’s string divider, Chien would be able to use sleight of hand and the top of his act to set up half of the table as blue cards and the other half as red cards.