What colors did Titian use
There are some excellent resources on Titian’s technique and palette, most of which are now available for free online:“Technical Examinations of Titian’s ‘Venus and Adonis’: A Note on Early Italian Oil Painting Technique,” by Ulrich Birkmaier, Arie Wallert, and Andrea Rothe http://www.getty.edu/conservation/publications_resources/pdf_publications/pdf/historical_paintings.pdf
“North and South: Painting Techniques in Venice,” by Jill Dunkerton. In Renaissance Venice and the North: Crosscurrents in the Time of Durer, Bellini, and Titian, edited by Bernard Aikema and Beverly Louis Brown (New York: Rizzoli Intl. Publishing, 2000), 92-103.
“Recovering Titian: The Cleaning and Restoration of Three Overlooked Canvas Paintings,” by Jill Dunkerton https://www.nationalgallery.org.uk/upload/pdf/vol-34-essay-2-2013.pdf
“Titian’s Painting Technique to c. 1540,” by Jill Dunkerton, Marika Spring, Rachel Billinge, Kamilla Kalinina, Rachel Morrison, Gabriella Macaro, David Peggie, and Ashok Roy
https://www.nationalgallery.org.uk/upload/pdf/vol-34-essay-1-2013.pdf
“’A Boy with a Bird’ in the National Gallery: Two Responses to a Titian Question,” by Paul Joannides and Jill Dunkerton
https://www.nationalgallery.org.uk/upload/pdf/joannides_dunkerton2007.pdf
“Titian’s ‘Bacchus and Ariadne’,” by Arthur Lucas and Joyce Plesters
https://www.nationalgallery.org.uk/upload/pdf/lucas_plesters1978.pdf
Dunkerton, Jill, Susan Foister, and Nicholas Penny. Dürer to Veronese. Sixteenth-Century Painting in the National Gallery. New Haven: Yale University Press, 1999.