Here is a scan of the two varieties known of the 25c chip from Silver Bird (formerly Thunderbird) on the Strip. Both are DIECAR mold but made with base chips of slightly different color. One is burnt-orange, other is red. TCR catalogs these as N2201 for the burnt-orange (the lighter one) and D0725 for the red. Both have 1976 use dates. Comparison of the edges shows no evidence of fading; these were definitely made with different color clay.

Only one of these varieties is pictured in The Chip Guide. I've submitted the pair to be shown for comparison there.

For sale for $15 for the pair, delivered in the USA.