In the end, it is best to let your taste buds decide how much dried oregano you should use in your recipe. Also keep in mind that a packet of dried oregano that has been lying on your shelf for several months provides less flavor than a packet of oregano that you have purchased recently.
You can certainly choose a CMYK or HSL dialog in the fill and stroke and all colour pickers, but it converts all colors to 8 digit hex as you willl see in the bottom of the picker. Since RGB and CMYK spaces are both device-dependent spaces, there is no simple or general conversion formula that converts between them.
The underlying color model in Photoshop is neither RGB nor CMYK but LAB. It has the widest gamut, which means it can hold more color values than any other model. Of the two other models, RGB has more color values than CMYK does. When you convert from RGB to CMYK, the program first maps the RGB values into the LAB colorspace. It then maps the LAB values into the CMYK colorspace. Now, for REAL entertainment...take a pure RGB blue, or a pure RGB green, and attempt to map it into CMYK colorspace. It doesn't work at all.