Sadly its not as easy as many people think, personally I do not recommend that you attempt it as often the results can be disappointing and sometimes unexpected. Just remember that re-dying leather is not an exact science, so experiment on an inconspicuous spot before working on the entire project.
There are several stages involved in the process -
1) DEGLAZING - Stripping off the old finish so that the surface can absorb the new dye.
2) CONDITIONING - Applying a conditioner to make the leather softer and more plyable, also helps to preserve the leather and nourish it. Fiebings four way is a good one to use.
3) DYEPREP - Cleans the surface leather to absorb the dye more readily.
3) DYING - Obviously applying the colour, for large areas I recommend either an airbrush or one of the preval disposable air brushes as it gives a more even colour. Several coats may need to be applied. As well as a base coat before applying the final colour.
For white leather you want to re-dye brown, first re-dye the leather light green.
For white leather you want to re-dye dark blue, first re-dye the leather light black.
For white leather you want to re-dye black, first re-dye the leather green or blue.
For red leather you want to re-dye black, first re-dye the leather green.
Dyeing your leather different colour can be done . However, it is very difficult, if not impossible, to dye leather a colour lighter than its current shade. Just like with dyeing hair, it is easiest to go from a light colour to a dark colour. All told, you will need about 32 oz. of dye to recolor a sofa or love seat, as well as 8 to 16 oz. of additional dye to adequately cover a matching leather chair or recliner, if you have one. I add this because costs can soon escalate.
4) FINISH - This locks in the colour and stops it from running/seeping into clothes, skin, pets, children :) . There are several types available depending on what you want, for a high gloss there is Supersheen, the Fiebings spray contains a wax that helps to waterproof the whole or a satin sheen for less of a gloss. There is also Fiebing's resolene, that can be buffed to a glossy finish.
Motorcycle Suits - The coloured panels sometimes have a strong dirt resistant layer that resists new dye. It might be possible to cut through this with "Deglazer".
Thread - If your article has been sewn with synthetic thread, this will not accept the dye. If you attempt a change of colour, you may be left with a contrasting thread.
After Dying If the surface of your leather has offered any resistance, the new dye may not be fully absorbed and might leave a dusty deposit. This should be removed by rubbing with a clean cloth until no staining of the cloth occurs.
Suede The surface should be prepared by using "Suede Cleaner" to remove any grease spots and dirt. It is not possible to seal the surface without loosing the nap. It will help to rub the surface with a clean rag when the dye is dry and then apply a spray of "Scotch Guard".
Through out the whole process, latex gloves and a disposable apron are a good idea, as it will save your hands turning the same colour as your leather :) And believe me its hard to remove it from skin!!
All the best and good luck
The Larp Emporium