Thanks for your speedy replies 🙂
As a total Illustrator newb, I tried to take the image out to Photoshop, add a layer overlay or effect and then copy back to Illustrator, BUT (and this is probably me missing something) the copy only copies the layer, not its overlay or effect.
In the end, I opted for Illustrator’s Edit Colours>Adjust Colour Balance option and got to as near to the colour I wanted as to be just fine for my purposes.
Thankyou once again for your suggestions. Much appreciated. Tim.