There is a timeline with a set. The set is changing a property in the object and the value of the property is empty string. When we jump to the end of the timeline, the color property set to #ffffff, but when we jump back to .progress(0), the value become RGBA(0,0,0,0). It seems like GSAP tries to interpret the target value as color and decides to use RGBA(0,0,0,0) as the original value.
I think in this case GSAP should reset the value back to empty string on .progress(0).