What do old diamond color terms like Wesselton and Jager mean?

Wesselton and Jager are legacy color grade names from an older diamond grading system, now replaced by the IGI and GIA letter scale running D through Z. The letter scale divides colorless diamonds into six descriptive bands: finest white, fine white, white, lightly tinted white, tinted white, and tinted color. Each band maps to specific letters: D and E are finest white, F and G are fine white, H is white (the old Wesselton), I and J are lightly tinted white, and K through Z carry increasing yellow presence.
For lab-grown diamonds, IGI certification uses this same D-Z scale, so every Valquère stone carries a precise, internationally readable grade. At H color, yellow tint is nearly invisible without a side-by-side comparison to a whiter stone, making G-H the practical sweet spot for buyers who want a clean white appearance without paying for imperceptible differences. Grades D through F are the most colorless available, but the visual gap between D and G is difficult to detect in a set stone. Knowing where a grade sits on the letter scale tells you more than any legacy term ever did.