I think I may have solved my own problem. Well, worked out the problem anyhow, I'm not sure about the solution.
It appears that the edges of the quad are being affected by the colours of the texture outside the u,v coordinates. By making sure the direct edges are the same colour as the area of the texture to be drawn, I eliminate this problem.
It seems no amount of repositioning u,v coordinates is helping, though I might be doing it wrong. I've tried calculating the coordinates and offsetting them 0.5 from their original position before getting u,v values, but this doesn't have any affect.
It appears that the edges of the quad are being affected by the colours of the texture outside the u,v coordinates. By making sure the direct edges are the same colour as the area of the texture to be drawn, I eliminate this problem.
It seems no amount of repositioning u,v coordinates is helping, though I might be doing it wrong. I've tried calculating the coordinates and offsetting them 0.5 from their original position before getting u,v values, but this doesn't have any affect.