How to change line color based on data range in r plotly -

i trying create plotly line graph can change color based on value threshold. unable find option in r plotly. below code:

p2 <- plot_ly(mdata1, x = ~ttime, y = ~value, type = 'scatter', mode = 'lines',  color= list(~entity_name,fill.color= ()) , fill = 'tozeroy') %>%       layout(xaxis = list(title = 'date',showticklabels = false),              yaxis = list(title = 'memory percentage'))