Pickle label under shop lighting
A self-help group in Cuttack is printing a label for its bottled mango pickle. The label is 8 x 12 cm, printed by four-colour offset on white paper. The current artwork uses a deep red logo (C0 M100 Y100 K10), a bright green band (C100 M0 Y100 K10), and a slogan in gold (C20 M30 Y80 K0) on a cream background (C5 M5 Y20 K0). In the shop, under warm LED light, the red looks brown and the green looks olive; at the same time the red logo appears to vibrate against the green band. The gold slogan almost disappears when the bottle is seen from two metres. The group wants the label to look premium and to keep the red and green identity. They can afford one spot colour but not more.
1. Explain why the red and green vibrate and why the gold slogan disappears. Separate the lighting effect from the ink contrast effect.
Read the worked answer
Red and green are near-complementary. When placed edge to edge at similar value and saturation, the eye's colour-opponent channels are stimulated unequally and produce simultaneous contrast, so the boundary appears to shimmer. The gold slogan fails for a different reason: gold (C20 M30 Y80) and cream (C5 M5 Y20) are close in value, so at two metres edge contrast falls below what the eye can resolve; the slogan is visible only by hue, and hue differences blur first at distance. Warm LED light also shifts the appearance of printed inks because the illuminant has a different spectral power distribution; reds can look brown and greens olive. Do not diagnose this as wrong colours alone; separate the illuminant effect from the ink contrast effect.
2. Recommend changes that preserve the red and green identity while fixing both problems.
Read the worked answer
Separate the red and green with a dark keyline or a white gap of at least 2 mm at label size. Change the slogan from gold to a dark brown (for example C40 M60 Y80 K40) or deep maroon so its value is clearly darker than cream; do not rely on hue alone. Use the one affordable spot colour for the brand red, because a spot red holds its identity better than a four-colour build under varying shop light; keep green as CMYK. Darken the green band slightly so the red logo sits on a mid-value field, not an equal-value field. Proof under warm and cool light and view at 2 m.
3. Why should the printer not simply receive an RGB file for this label?
Read the worked answer
RGB is for screen, CMYK for process print. The file must be supplied in CMYK with any spot colour named, and the red must be checked against a printed swatch, because a saturated RGB red converted to CMYK loses chroma and may print orange-brown. Small black text should be set as 100% K, not four-colour, to avoid registration blur.