Sunflower and a bright yellow is the Mellow Yellow Dream 
I use Gildan Softstyle HEATHER style tees (65% Poly/35%Cotton) or Gildan 100% cotton. At times I have to use other brands such as Port & Company, Delta, Bella canvas.
Care Instructions
-Machine wash, inside out, with cold water and mild detergent
-Hang to dry (recommended) or tumble dry inside out on low
-Do NOT bleach - Do NOT Use Fabric Softener - Do NOT iron directly on design