Can you be more specific on the colour issue ? Is it darker than the growing hair ? [ it will lighten up a bit after washing and oxidation] Thinning is possible ...best way is by using a hair-removal cream..go easy with it initially...not all the hair sheds out immediately after application... do it over a number of days, because once it`s gone you can`t put it back !
http://www.youtube.com/watch?v=rPULkcyVD2Y
I wouldn`t waste money buying multi-packs of colouring products..you could simply pop into a `Normal` high-street [ladies] hair salon just tell them you`d like to deepen your hair a shade or two and ask them to recommend a particular over-the-counter product... Lòreal and Wella do them ... they could tell from looking at your hair,what shade to buy--- try a 10-minute application, before rinsing out [despite what it says on the box] ...have a look when it`s dry....repeat if necessary, until you achieve the desired depth of colour.