I will be looking to change my front sight (lyman globe) to a silver or brass blade,seem the hood on the lyman globe makes it hard for me to see the front sight.I was wondering which color would be better silver or brass color for hunting in low light conditions???

Sounds like you're shopping for an old time sort of sight, otherwise a fiberoptic bead set in a square post is jump out at you obvious. If you want a sight made of authentic materials then it depends a little on the game you are laying the sights upon and the colour of the surrounding terrain. FWIW I just replaced a silver front sight on my Fusil de Chasse with a brass one.

I wouldn't go with the silver. If you are looking for a good solid front sight of the old school, then look for a gold faced (brass?) blade cut at an angle (I know it reflects light). Beads break off, and solid silver/brass blades are hard to see in some lights. The slanted cut will pick up light while hunting in dense cover, and can be smoked to provide a flat black post for informal target practice. My .02

Gold face blade ,any idea were to purchase one,the rifle is a 45-70 B.C. with a rear upgrade lyman peep set-up

I don't have a ready source, see them on eBay from time to time. Here is another style that works well, known as the Sheard bead. http://www.rarewinchesters.com/gunroom/1894/M94-0889043/08.JPG These are sturdy, those I don't like are the "glued" on dots. An imbeded one would be ok, but still not my choice.

Be aware that many "silver" sights are not silver but rather some other metal as in "German Silver". I use coin silver sight blades in my muzzleloaders and my old 1908 Mannlicher-Schoenauer had a real silver bead front sight too. There is a significant difference in the appearance of the silver sights at dusk or dawn and thicker is better too. If you can rub rour thumb on it and the tarnish comes off as on true silverware, that's the quality you need. A big fat real ivory bead is pretty good too.