I'm pretty sure your plant is Ocimum tenuiflorum, commonly known by many names,but usually Holy Basil; Tulsi is also one of its common names.
I rather wonder if its potbound - turn it out of its pot to check and when you do that, remove the Plectranthus and pot it up separately. You may want to extract some of the seedlngs and pot those up, or just remove them if the rootball is solid. If it is potbound, that would explain the yellowing colour of the leaves, and a larger pot is called for, obviously. I don't know what the temperatures are like during winter where you are, but this plant is a woody perennial only in tropical regions, so the south east asian tropics are where it would be perennial - but if your temperatures cool down, then growth might slow down and the leaf colour be less vibrant. The other reason for less than optimum leaf colour is the fact its flowered recently; many plants look somewhat 'tired' after flowering, especially in pots and if they're putting energy into making seed because the spent flowerheads are still present.
If its not potbound, then cut back the flowered stems and give it some balanced fertilizer, something with an NPK of 7-7-7 if possible, if you can get anything like that where you are. It's still a good idea to remove the other growth in the pot, to allow the Tulsi its own root space; the Plectranthus will also need root room of its own in a separate pot anyway. Cut back the flowered stems even if it does need a new pot, unless you want to save any seed.