Mapping a list of cells in seurat featureplot
To color the TSNEPlot, you can generate a new column in metadata with the expression levels (High, low, etc). Then use pt.shape to set a shape for each identity.

To show binary expression based on expression you first have to define the list of cells that are below or over your threshold. Once you have those lists you can use SetIdent() in Seurat to color those groups. 

load(file= "~/seuset_16.RData")

high &lt;- c("s1.1","s1.4", "s1.80")  
low &lt;- setdiff(colnames(seuset_h16@data), high)  
seuset_h16 &lt;- SetIdent(seuset_h16, cells.use = high, ident.use = "high")  
seuset_h16 &lt;- SetIdent(seuset_h16, cells.use = low, ident.use = "low") 
seuset_h16 &lt;- StashIdent(seuset_h16, save.name = "expr")  
seuset_h16 &lt;- SetAllIdent(seuset_h16, id="res.1")  
t &lt;- TSNEPlot(seuset_h16, pt.size = 2, do.return = T, pt.shape ="expr")  
t




high &lt;- c("s1.1","s1.4", "s1.80")  
low &lt;- setdiff(colnames(seuset_h16@data), high)  
seuset_h16 &lt;- SetIdent(seuset_h16, cells.use = high, ident.use = "high")  
seuset_h16 &lt;- SetIdent(seuset_h16, cells.use = low, ident.use = "low")   
t &lt;- TSNEPlot(seuset_h16, pt.size = 2, do.return = T, colors.use = c("red", "grey"), do.hover =T, data.hover =c("ident", "res.1))  
t