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In the following example there are orange text links and an orange button with white text, that have low colour contrast (in this case a contrast ratio of 3.1:1 which is well below the recommended minimum of 4.5:1):
In the next example, there is a the green button with white text that has shows good colour contrast (with a contrast ratio of 4.9:1 which is above the recommended minimum of 4.5:1):
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