The attribute that places a color on the spectrum, independent of how light or saturated it is: red, orange, yellow, green, blue, violet.
Keep the hue fixed across all five surface colors and vary only lightness. That’s what keeps the panels feeling like one material.
Hue is what civilians mean by “color,” so using it precisely is the cheapest upgrade in design crit: “shift the hue toward green” names one dial, “make it more minty” spins three at once. Mind the tooling, though. HSL’s hue wheel is perceptually lumpy, so equal hue steps don’t look equal (OKLCH’s do). A palette survives almost any adjustment to saturation and lightness; move a hue and you’ve touched the brand.