Every colour-retention finish we use is undone by the same three mistakes: hot water, wringing, and direct sun. None of them are complicated to avoid, which is why this note is short.
The method
Cold machine wash, always. Heat is what pulls dye out of cotton fibres fastest — a warm wash will fade a dark shirt over a handful of cycles in a way a cold one will not manage in a year. If your machine defaults to warm, change it once and leave it.
Skip the wring cycle where you can, or keep it short. Twisting wet cotton under tension is what breaks down the weave early and leaves permanent creasing along the twist lines. Let gravity do the work instead.
Dry in shade, not sun. Sun does to colour outdoors what heat does to it in the machine.
Hang the shirt on a proper hanger rather than folded over a line — it keeps the shoulder line from creasing and dries faster than you would expect out of direct light. A warm iron on the reverse, once dry, is enough to finish it; you should not need starch or a hot setting on any of our cotton.
That is the whole method. Cold water, minimal wringing, shade. Do those three things and the finish holds for years, not washes.