How can add my own color palette in Sakura terminal?
I use Ubuntu 12.04, and in options menu, I see only
rxvt palettes available.
i think you'll need to Xdefaults; this page explains it as well as providing some examples; https://wiki.archlinux.org/index.php/X_resources
several other terminal emulators (terminator, xfce-term) support adding your own colours, on the fly, using a colour picker. This can be useful to preview your own selection and export your Xdefault colours to the term of your choice.
Palletes are hardwired in the source code, but reasonably simple to modify. Just download source and modify the constants for given colors. Palettes are defined at the beginning of sakura.c and contain colors in GdkRGBA style.
Adding a new palette is more difficult, as the names of palettes are used several times in the source.