They used to be displayed in the public promotional displays in Legoland Windsor back in early 2001.
You can see all the masks allocated to their wearers. The light blue Kaukau belonged to Kopaka (to match his eye stalk) and the yellow one is Pohatu (because yellow is close to the sand-ish colors). Light blue was probably too close to regular blue and may have confused consumers, so they changed it to icy clear color. Pohatu’s yellow was changed to trans neon-orange to match his eye stalk. Ruru and Matatu were changed to match the rest of Turaga masks.
These masks being “misprints” is easily one of the most widespread misconceptions in the community.