How to find out the current color theme in emacs

There isn't the concept of a current theme, and indeed, multiple themes can be applied in sequence to additively define the set of active faces. Support for theming was added into the latest Emacs versions (see M-x customize-theme), and there's still the option to "Select more than one theme at a time".

In short, when you activate a theme, you're not switching to that theme, but rather applying the changes specified in the theme to the faces and variables it lists.

All customizations which aren't explicitly placed in a named theme are actually put into the hidden user theme, so there's always at least one active theme. The other currently enabled themes are listed in the variable custom-enabled-themes.

Share an example for using color-theme-print to get what theme I applied.

via M-x color-theme-print you will get outputs about the color theme info, then find a typical value that is unique for different color themes, I choose background-color whose value is 537182 for my emacs.

Open the color theme library color-theme-library.el then search the file with keyword as '537182', then you'd get the theme name there.

Although not a straight-forward way but it really works, hope that helps!

M-x color-theme-print is useful to tell you exactly which font faces are in effect. It won't tell you which named color themes have been applied, but you should be able to work that out from your init file. If not, I suppose you must be using a mode that applies its own color theme (I know Proof General does this, and most irritating it is).