Who handles the warranty on these. They are Colts, but made by Walther and distributed by Umerex.
They are made by Umarex (at the Umarex factory in Arnsberg, Germany), not Walther. Umarex owns a large stake in Walther and likes to slap the Walther name on a lot of their pistols.
That said, what did the warranty documentation with the pistol say? Typically, true Colts have a one-year warranty on the finish and a lifetime warranty on the pistol.