Explanation:

In WTO terminology, subsidies in general are identified by “Boxes” which are given the colours of traffic lights: green (permitted), amber (slow down — i.e. be reduced), red (forbidden). In agriculture, things are, as usual, more complicated.

The Agriculture Agreement has no Red Box, although domestic support exceeding the reduction commitment levels in the Amber Box is prohibited; and there is a Blue Box for subsidies that are tied to programmes that limit production.

The 'amber box': for agriculture, all domestic support measures considered to distort production and trade (with some exceptions) fall into the amber box.

The 'green box': In order to qualify for the "green box", a subsidy must not distort trade, or at most cause minimal distortion.

The 'blue box': The blue box is an exemption from the general rule that all subsidies linked to production must be reduced or kept within defined minimal ("de minimis") levels.