noun
registration black
Printing term: a solid black made by overlaying all four CMYK inks, used for registration marks and rich black.
トンボには四色ベタを使います。
Registration black is used for crop marks.
リッチブラック is a general term for deep black made from CMYK, while 四色ベタ specifically refers to the 100% overlay of all four colors, often for registration.
トンボ are the crop marks themselves; 四色ベタ is the ink color used to print them.
Compound of 四色 (four colors) and ベタ (solid fill), referring to a solid area printed with all four process colors.