Yuru Log Pre-inked Stamp

I enjoy using stamps to mark off the days in my calendar, and up until now I had only used one stamp that used black ink. Now with these colorful stamps, I find myself looking forward to marking off a new day because they're so cute and colorful! They work very well on my calendar, but unless being used on plain white paper, I don't think the ink shows up very vibrantly (I tried to stamp them on the brown paper bag I got them in). For my purposes, these stamps are 5-star, but if anyone was hoping to stamp these on darker paper or skin, they don't show up as well (or at all in the case of skin; I tried that too).