I have tried to add a colour to an EDTA solution, adjusting the pH using citric acid. At concentrations from 5% down to 2% (EDTA), however the colour appears to 'bleach' out after only a couple of hours in sunlight. The solution also contains a surfactant (nonionic) at 10%

I have tried varying the colour, using blues, orange, red, pink and all lose colour extremely fast.

Ideally I want the pH to be 7 or 8 at most, I have tried both with no change to the outcome.

The level of EDTA is high, but in use the solution will be diluted by around 400:1 with water.

Is there any way to hold the colour in such a solution?

Edit:

I have just tried neutralising using Phos instead - will post tomorrow if successful.