<?php
$string = 'ABCDEF
Colore lato A: NO
Colore lato B: Colore lato B (+3,00)
Colore lato C: NO
Stampa lato A: Stampa lato A (+7,00)
Stampa lato B: NO
Stampa lato C: NO
blablabla
blablabla';
$result = preg_replace('/' . PHP_EOL
. '?^(Colore|Stampa).*NO|^(Colore|Stampa).*:\s*/m', '', $string); echo $result;
PD9waHAKCiRzdHJpbmcgPSAnQUJDREVGCkNvbG9yZSBsYXRvIEE6IE5PCkNvbG9yZSBsYXRvIEI6IENvbG9yZSBsYXRvIEIgKCszLDAwKQpDb2xvcmUgbGF0byBDOiBOTwpTdGFtcGEgbGF0byBBOiBTdGFtcGEgbGF0byBBICgrNywwMCkKU3RhbXBhIGxhdG8gQjogTk8KU3RhbXBhIGxhdG8gQzogTk8KYmxhYmxhYmxhCmJsYWJsYWJsYSc7CiRyZXN1bHQgPSBwcmVnX3JlcGxhY2UoJy8nIC4gUEhQX0VPTCAuICc/XihDb2xvcmV8U3RhbXBhKS4qTk98XihDb2xvcmV8U3RhbXBhKS4qOlxzKi9tJywgJycsICRzdHJpbmcpOwplY2hvICRyZXN1bHQ7