Description:
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We know that `pdf_setcolor()' currently accepts 7 parameters:

bool pdf_setcolor ( resource p, string fstype, string colorspace, float c1, float c2, float c3, float c4 )

If I pass 'rgb' as colorspace (3rd parameter), the function asks for `float c4' (7th parameter) which is not needed.

Reproduce code:
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pdf_setcolor($pdf, 'both', 'rgb', 0.7, 0.7, 0.7);

Expected result:
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The code above does not work.

This code works:

pdf_setcolor($pdf, 'both', 'rgb', 0.7, 0.7, 0.7, 0.7);