Using ph indicator

[kubota]

Just checked ph on a winoes wash that seems a bit slower than i usually get, using hydroponic ph indicator.
The reading was 4.5 and all was looking good, however after leaving the test sample on the bench for 30 mins the colour changed to give a reading of ph 6.
Is this normal or what? every other time after i check the ph i have dumped the sample straight away, so i don't know if the early colour is the right one to read or after it has sat for a while.
According to the bottle instructions you should get a reading after shaking the mix.
I was surprised to see the sample go from a nice pink to a light orange after a period of sitting.
Anyone noticed this when doing tests on ph?