It’s not true. You’re wrong.
The colour of the civil engineer’s helmet on site is white and not yellow. That is the convention.
The purpose is to differentiate the engineer from other professionals on site. Every other kind of professional has a different colour helmet on site. The yellow one is for labourers skilled and unskilled both. Giving yellow helmet to engineers is disrespect in a sense.
An engineer must always demand or arrange for a white helmet for himself on site.