Ask for the complement of red and you get two different answers depending on which wheel is being consulted. The wheel taught in art classes puts green opposite red. The wheel a screen works in puts cyan there.
Neither is wrong. They describe two different physical processes, and the disagreement is the reason a palette that looked right on paper can look wrong in a browser.
Why are there two wheels?
Because paint and light combine in opposite directions. Pigment works by subtraction — each layer removes wavelengths, so mixing everything heads towards mud. Light works by addition, and mixing full red, green and blue gives white.
| Artist’s wheel | Screen wheel | |
|---|---|---|
| Primaries | red, yellow, blue | red, green, blue |
| Opposite red | green | cyan |
| Opposite blue | orange | yellow |
| All mixed | dark, muddy | white |
Every palette tool that works in hue degrees is using the second wheel, because that is the one the hue value describes. Adding 180 to a hue gives the additive complement, and it will not match the colour a paint chart calls the complement.
For screen work the additive answer is the correct one. It is worth knowing the other exists so that a printed reference and a generated palette disagreeing does not read as a bug.
The two wheels also order their hues differently, which is why a hue number cannot be translated between them. On the screen wheel the sequence from 0 degrees runs red, yellow, green, cyan, blue, magenta and back to red, with the secondary colours falling at the sixty-degree marks. Yellow at 60, cyan at 180 and magenta at 300 are worth committing to memory, because they anchor everything else.
What do the harmony names mean?
Angles, and nothing more mysterious than that. Each scheme is a fixed rotation around the wheel from a starting hue.
| Scheme | Hues |
|---|---|
| Complementary | base and +180 |
| Analogous | base, +30 and −30 |
| Triadic | base, +120 and +240 |
| Tetradic | base, +90, +180 and +270 |
| Split complementary | base, +150 and +210 |
Analogous schemes are the calm ones because neighbouring hues share wavelengths and never fight. Complementary schemes are the loud ones for the same reason in reverse.
Split complementary is the compromise worth knowing. It keeps most of the tension of a complementary pair while stepping either side of the exact opposite, which removes the harshest part of the effect.
Saturation is the variable that decides how a scheme feels, and it is not part of any of these definitions. The same triadic set at full saturation reads as a children’s toy and at a third of it reads as a considered brand — identical hues, entirely different result. Choosing the angles is the quick decision; choosing the saturation and lightness is the one that takes the time.
Why does a complementary pair vibrate?
Because two fully saturated opposites at the same lightness give the eye no edge to settle on. The boundary appears to shimmer, and text set in one colour on the other is genuinely hard to read.
The fix is never to abandon the pairing. It is to separate the two on lightness rather than only on hue — a dark version of one against a pale version of the other reads cleanly — or to put a neutral between them.
This is the reasoning behind the common proportion advice: one colour dominant, one supporting, one used sparingly as an accent. The accent works precisely because there is little of it.
What are numbered scales for?
Removing the judgement. Systems that number their steps give every hue the same set of stops, so swapping a brand colour means swapping one row rather than rethinking every usage.
The numbering is a convention rather than colour theory — a low number is pale, a high number is dark, and the middle of the range is where the base colour sits. Two systems using the same idea do not use the same steps, so the numbers are not portable between them.
What is portable is the discipline. A palette with named steps is one where a component can specify "the border step" and stay correct after a rebrand.
How many colours does a brand need?
Fewer than most palettes contain. One primary, one accent, a neutral ramp and the states that carry meaning — success, warning, error — covers nearly every interface.
The states are the ones people forget to plan and then invent inconsistently. Deciding them at palette time means they belong to the same family as everything else rather than arriving as three unrelated imports.
Everything else is variation on those, which is a generation problem rather than a design one.
Questions people ask
Do harmony rules guarantee a good palette? No. They generate defensible starting points, and the choice of lightness and proportion does the rest.
Why does my triadic set look garish? All three are probably at full saturation. Drop two of them and the third carries the scheme.
Are warm and cool objective? The split is conventional — reds through yellows warm, greens through blues cool — and the edges are a matter of taste.
Does hue order matter in a gradient? Yes. Going the long way round the wheel passes through hues neither endpoint contains, which is where a muddy midpoint comes from.
Start from one hue and rotate. The colour palette generator covers the schemes together, with complementary, analogous, triadic and tetradic each on their own, while the brand, Material and Tailwind scale generators produce the numbered kind.