If you want to show your fleeces, or have a large flock, you need to register with the Wool Board. However, if you have just a hobby flock, especially a coloured one, they're not interested. You would get a few pence each for the fleeces, and transport would be much more than that. This is why many people prefer to deal with fleeces themselves.
If you are a knitter or weaver, or have an outlet for yarn, then it could be worth getting them spun up, but if they are a variety of colours then somewhere such as the Natural Fibre Co would have to blend them into a grey, as their minimum order weight is 20 or 25 kgs. There are other Mills which will do individual fleeces, so you get your separate colours, but you would need to work out carefully if that would be financially viable. It's not a cheap option.
Have a look at some of the posts on this subject in 'crafts' for what you have to do to prepare fleece for sending to a Mill or selling direct to customers.
If carefully stored then one year's clip can be held over until the following year to give you enough for NFCo.