Попробуйте:
import seaborn as sns
import matplotlib.patches as mpatches
x=[1,1000,1001]
y=[200,300,400]
sns.set_context(rc={"figure.figsize": (8, 4)})
nd = np.arange(3)
width=0.8
plt.xticks(nd+width/2., ('1','1000','1001'))
plt.xlim(-0.15,3)
ax = sns.barplot(x=x,y=y)
colors = ['r', 'g', 'b']
labels = {
1:'x',
1000:'y',
1001:'z'
}
handles = []
for col, lab, patch in zip(colors, x, ax.axes.patches):
patch.set_color(col)
handles.append(mpatches.Patch(color=col, label=labels[lab]))
ax.legend(handles=handles)
plt.show()