The colour of the teeth is genetically determined.. It can be corrected by teeth whitening, but only temporarily.. It can also be corrected with Smile Designing, but that's too invasive a procedure just to change the colour of the teeth..
Next Steps
You can get a clean-up done on regular basis and consider whitening if some special occasion is coming up..
Health Tips
Please do not use a mouthwash for long.. It will in turn bring back staining..