What pH indicators are commonly used for non-polar medium?

Compounds, commonly used as [pH-indicators](https://en.wikipedia.org/wiki/PH_indicator), are soluble in aqueous media and polar solvents (DMSO, DMF, NMP etc.) and are functional pretty much across all these solvents. However, practically none these indicators are soluble in non-polar solvents (hexane, chloroform, dioxane etc.).


I briefly searched for the suitable available systems and so far there is only an article about oxoporphyrinogen derivatives used as pH-indicators in $\ce{CH2Cl2}$ [1]. Are there any other *common* substances that are typically used for the visualization of acid-base equilibrium in solvents with low polarity? 


### Reference


1. Shundo, A.; Ishihara, S.; Labuta, J.; Onuma, Y.; Sakai, H.; Abe, M.; Ariga, K.; Hill, J. P. *Chem. Commun.* **2013,** *49* (61), 6870–6872. [DOI: 10.1039/C3CC42859A](https://doi.org/10.1039/C3CC42859A).


