Why does dry HCl gas not change the colour of the dry litmus paper?

Why does dry HCI gas not change the colour on the dry litmus paper?

(a). What is produced if an acid is added to a base? (b). Why does dry HCl gas not change the colour of dry litmus paper? (c). What colour does phenolphthalein indicator tum when added to an alkali (such as sodium hydroxide)?

Dry HCl gas does not change the colour of dry blue litmus paper . Give reasons.

Dry hydrogen chloride gas does not change the colour of dry litmus paper. Why?