Posted: 17/07/2016 at 15:15
Loss of colour between veins is usually a sign of nutrient deficiency (iron, manganese or magnesium.) Have you been feeding it regularly? If not, try using a tomato feed as these generally include the trace nutrients mentioned above. As a short-term fix, spraying it as well as watering it in could be of benefit. In the longer term, mulching the area around the roots with well rotted farmyard manure in the autumn should provide for its needs.
If it's a new(ish) wall, there is also the possibility that lime from the cement is making the soil a bit on the alkaline side, making it harder for the vine to take up nutrients. Again, the FYM should help with that.
If only the oldest leaves are affected it could simply be those leaves are reaching the end of their life but a good feed would be a good idea in any case.