color list value offset support

src/mol-geo/geometry/direct-volume/direct-volume.ts

src/mol-geo/geometry/direct-volume/transfer-function.ts

src/mol-plugin-ui/controls/legend.tsx

src/mol-plugin-ui/controls/parameters.tsx

src/mol-util/color/color.ts

src/mol-util/color/palette.ts

src/mol-util/color/scale.ts

src/mol-util/legend.ts

src/mol-util/param-definition.ts