秘色 (hishoku in Japanese, mise in Mandarin) refers to the pale bluish-green celadon color of this piece. The word literally means "secret color", and it is said to have once been reserved as imperial wares.
Two possibilities for your flower vase marked 秘色 Hishoku assuming that this 秘色 is the same as 秘色窯造 Hishoku-gama (kiln) zō (made). One is a Chinese kiln called 秘色窯造, and the second is a Japanese maker by the same kiln name 秘色窯造 in the Shino-yaki ware 志乃焼. Example each is given below using examples from completed transactions.
13" x 4" this was posted on a site I am a member of and two gentlemen gave great interpretation of the vase. Will take locally and have an appraisal done.