The oil-soluble dye means a dye which can be dissolved as much as 1% by weight or more in any of aromatic hydrocarbons such as toluene and xylene, ketones such as cyclohexanone and methyl ethyl ketone, CELLOSOLVES such as ETHYLCELLOSOLVE, an ester such as ethyl acetate, ETHYLCELLOSOLVE acetate or tetrahydrofuran.