The fifth column has three hearts and since the colors alternate, nothing can go between the two that are given. The third heart must be a purple one above the green one. The rest of the squares in that column stay empty.
Next, look at the second column. There are six hearts so all of the squares will be full. They'll alternate yellow and red down from the top. Work on the bottom row next.
Good luck!

[/spoiler]

Blue Yellow skip skip Blue Yellow
Green Red Green Red Green Red
skip Yellow Blue skip skip Yellow
Blue Red skip Blue skip Red
Green Yellow Green skip skip Yellow
Blue Red Blue Red Blue Red
[spoiler]

Row 2 has 7 hearts which means the yellow heart in is the odd spaces. The even spaces can't be red (col 2) or green (col 5) so they're purple. Column 3 must now be R,Y,-, R, Y,-. Then work on column 2.

Have fun!

[/spoiler]
B R X B X R B R
Y G Y G Y G Y G
X R X X X X B R
B G X B G X X X
Y R X X Y R Y X
B G B X G X B G
X R X X X X Y R
Y G Y G Y G X X
[spoiler]

[/spoiler]
G X R G R X G
Y B Y B Y B Y
G R X G R X G
X B R B X X X
Y R Y X X R Y
G B X G X B G
[spoiler]