The fonts are updating, that's all. The update to text layers doesn't occur until you insert the cursor into the text. As soon as you click, the fonts get updated and it seems you aren't using the same font, or the same font from the same foundry, as the original.
Traditionally you would see a warning that a text update is going to occur. However, if you saw that warning at some point and clicked the "Don't show this again" box, you may not see the warning.
There could be many reasons why the font updates to a different display...
A typeface named "Futura" from Linotype, is not the same thing as a typeface named "Futura" from ITC, which is not the same as a typeface named "Futura" from Adobe, etc. It's very possible to use a font with the same name, but have it display differently.
A font conflict on your system can cause auto-replacement of an undesired font.
It's possible to have the correct font installed, but be missing a face for that font. So if the original type is set in "Futura Semibold" but you do not have the "semibold" face installed, the type will update to merely "Futura Regular", "Futura Medium", "Futura Book", or some other face since the necessary face is missing.
To me, the type doesn't "turn more grey". It merely decreases in weight going from a bold/semibold/demibold to a normal or regular weight.