Making a plot cleaner
It doesn't look like this data has been clustered, and you are plotting the 'value', rather than the cluster. If you want to represent values on a tSNE using Seurat, a better function to use is the FeaturePlot, which will colour the points in a more meaningful colour gradient based on their value.
[It's possible this function wasn't available at the time this question was written]
If, instead, you want to plot clusters, then you should carry out some clustering on the data first using FindNeighbors/FindClusters.
There's a great introductory tutorial to guide you into using Seurat on the Satija lab page:
https://satijalab.org/seurat/articles/pbmc3k_tutorial.html