you should post your image on the forum, rather than link to it.  Also youll get more help if the image is neither scaled, nor a jpg.

Your grass tile is too noisy.  Simplify it and decrease the contrast.  It also doesnt tile very well, the tile boundaries are very obvious.

There are a number of ways to make a character stand out.  One would be outlines, but there are other ways.  You can use hue, value or saturation. 

To do it using hue you would make sure the colors in the character are different from the background.  For example, use more warm colors, if the background uses more cool colors.  This might not be practical if you have many different backgrounds though.

Saturation might work.  Example, all the tiles you can walk on are relatively less saturated than the character.  Doesnt have to be very extreme.  You can do this on a case by case basis for each tile.  Like if you want to make lava, you dont need to desaturate it, because the red would already contrast with the characters color scheme.