Hi Ace
I agree it's a phosphorous deficiency but feeding with bone meal or any other powderd feed to the soil will take forever for the plant to get the nutrient
Try any off the shelf general purpose liquid feed which contains a good level of P (and N & K) and water it on in the evening using a fine rose at the recommended dilution but over the leaves, not just into the soil. This way the plant will absorb the nutrient more quickly.