Eigentlich hört sich das ganz stimmig an:
The TIE fighter design was first established in a concept model by Colin Cantwell. The simplified model defined the TIE's most distinctive features -- its ball cockpit and twin hexagonal wings. Subsequent sketches built up the TIE's form. Limitations in visual effects technology at the time dictated that Cantwell's blue color scheme be replaced with a more bluescreen-friendly gray. As the classic trilogy progressed, the TIEs regained a bit of their blue hue, although use of that color was fairly muted.