The colour of the xerox copies doesn't really matter. You can take black and white xerox copies or coloured xerox copies, according to your wish. But yes, you have to  carry your original certificates with you for document verification as this is an important step in every admission process. So, don't take stress about the colour of the xerox copies. You can carry anyone of your choice as it is not that much important.

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Xerox copies are to be attested and uploaded. There is no need to attest original documents. These are the documents you are supposed to get attested.  It will be eligible since BW or color Xerox won't make any difference. The authorities only require documents for proof and future reference and since you have got all the documents attested there is no such need to worry about. Getting documents attested add more value and evidence to the documents.

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