static float rainbowfox = 0;
rainbowfox += 0.0001;
if (rainbowfox > 1.f)
rainbowfox = 0.f;
auto cl = Colors::FromHSB1(rainbowfox, 1,1); //hue, saturation, brightness
ImGui::GetStyle().Colors[ImGuiCol_Separator] = ImVec4(cl.red(), cl.green(), cl.blue(), 1.0f);