Since you have cories and fine grain fertilized substrate will do good with plants. Keep in mind having a planted tank needs nutrients to thrive and depending on how advance with planting you want you may need co2 as well depending on how many
WPG (watts per gallon) your lighting fixture have. I suggest having nutrient based substrate that are so your cories can dig in them

I use eco-complete and the cory's love it. There is also carib sea sand or floura max onyx sand which is black. There's a lot you can choose from, here's a product line from caribsea
http://www.caribsea.com/pages/produc...nted_aquar.htm there also adashop
http://www.adgshop.com/Substrate_System_s/1.htm but if your only getting into serious
aquascaping b/c they're substrates are expensive! I'm sure there are other brands but these are the ones I can think of atm.