Вот некоторое решение Вашего вопроса:
только уже через реестр HKEY_CURRENT_USER\Software\Corel\CorelDRAW\17.0\Draw\Application Preferences\WindowScheme\PageMatColor - сменить дефолт на
Case 15987699 col = "Gray 5%"
Case 15132390 col = "Gray 10%"
Case 14737632 col = "Gray 12.5%"
Case 14277081 col = "Gray 15%"
Case 13421772 col = "Gray 20%"
Case 12632256 col = "Gray 25%"
Case 11776947 col = "Gray 30%"
Case 10921638 col = "Gray 35%"
Case 10526880 col = "Gray 37.5%"
Case 10066329 col = "Gray 40%"
Case 9211020 col = "Gray 45%"
Case 8421504 col = "Gray 50%"
Case 7566195 col = "Gray 55%"
Case 6710886 col = "Gray 60%"
Case 6316128 col = "Gray 62.5%"
Case 5855577 col = "Gray 65%"
Case 5000268 col = "Gray 70%"
Case 4210752 col = "Gray 75%"
Case 3355443 col = "Gray 80%"
Case 2500134 col = "Gray 85%"
Case 2105376 col = "Gray 87.5%"
Case 1644825 col = "Gray 90%"
Case 789516 col = "Gray 95%"