Preamble: I am not using yeelight myself.
However, for other systems, not all controls are available for all devices; and in most other cases you cannot mix and match the brightness and the color channels in all bulb modes. For yeelights, please see here: https://www.openhab.org/addons/bindings/yeelight/#channels
You don’t tell us which yeelight you are using (please read: How to ask a good question / Help Us Help You) but in the docs (first link) it states that brightness is available on thing type dolphin and ceiling; and color is available on thing type wonder and stripe.
I have other bulbs (different manufacturers) where I can use brightness only if the bulb is in white mode and need to adjust brightness with the colorpicker when the bulb is in colormode.
Judging by the docs and taking it all together, the yeelights do not offer different modes, but it appears that you have to use the controls in the following combinations:
- Yeelight LED White Bulb (Thing type
dolphin): usebrightnessNOT color - Yeelight LED Color Bulb (Thing type
wonder): usecolorNOT brightness - Yeelight LED Color Stripe (Thing type
stripe): usecolorNOT brightness - Yeelight LED Ceiling Light (Thing type
ceiling): usebrightnessNOT color