there's a whole operating system to play with, and all you are busy with is complaining that 9front doesn't have a grub theme.
i will repeat cinap here, cause it seems like realizes there are real solutions provided: > or you start the kernel from another kernel using the > reboot!kernelpath!method... on the bootargs prompt. you can do this from a GRAPHICAL system, from inside rio for example, or even make your own GUI.