This page explains it very well : www.nthuleen.com/teach/grammar/adjektivendungenexpl.html . Read it, keep it at hand, and refer to the flowchart each time you encounter an adjective here, and you will learn these declensions before you realize it!
I am still confused according to table http://german.about.com/library/weekly/aa030298.htm
it is plural so it should be schwarzen.
If the sentenced used a plural definite or indefinite article (die, keine, meine, alle, etc.) before the adjective, then the adjective automatically uses the -en declension. This Wikipedia article explains it a bit more clearly: