There are various issues that revolve around this fact.
1. Firstly why do you think that fairness is a sign of health / beauty / hansomeness etc when it is morre important to have a disease free healthy skin.
2. If every one in society thinks like this - where are we heading??!!!
3. Fairness injections may work in improving your shade of colour - but how long will you take those injections?
4. Cost factor/side effects may be involved too.
5. Best treatment would be regular use of sunscreen and some skin lightening creams or peel treatment for more even skin tone.
In any case see a qualified dermatologist near you before u take the plunge. further queries may be sent on follow up messaging. warm regards