matplotlib scatterplot x axis labels

You can do it like this.

plt.scatter(x="X", y="Y", c=df.color)
plt.xlabel("X axis label")
plt.ylabel("Y axis label")

That looks like a strange bug with pandas plotting to me! Here's a way around it:

fig, ax = plt.subplots()
df.plot(kind='scatter',x='X', y='Y', c='C', ax=ax)
ax.set_xlabel("X")
plt.show()

This will give you the graph you expect: