After plotting the graph according to the conditions, you must use the if statement to plot or make the warning message disappear. However, once the warning message is plotted, it does not disappear. Below is the corresponding code.

import os
from vcd.reader import TokenKind, tokenize
from vcd.writer import VCDWriter
import matplotlib.pyplot as plt
import matplotlib.animation as animation

def read_vcd(file_path):
    signals = {}
    current_time = 0

    with open(file_path, 'r') as f:
       for token in tokenize(f):
           if token.kind == TokenKind.TIMESTAMP:
                current_time = token.value
            elif token.kind == TokenKind.CHANGE_SCALAR:
                if token.reference not in signals:
                    signals[token.reference] = []
                signals[token.refe
rence].append((current_time, token.value))

    # Fill missing data points
    for ref in signals:
        filled_signals = []
        last_value = '0'
        for time in range(1, current_time + 1):
            if signals[ref] and signals[ref][0][0] == time:
                last_value = signals[ref].pop(0)[1]
            filled_signals.append((time, last_value))
        signals[ref] = filled_signals


    for ref, data in signals.items():
        print(f"Signal: {ref}")
        for time, value in data[:10]:  # 첫 10개의 데이터만 출력
            print(f"Time: {time}, Value: {value}")

    return signals

def write_vcd(signals, output_file):
    timescale = '1 us'
    with open(output_file, 'w') as f:
        writer = VCDWriter(f, timescale=timescale, date='today')
        refs = {}
        for ref in signals:
            refs[ref] = writer.register_var('scope', ref, 'integer', size=8)
    
        for time in range(1, len(next(iter(signals.values()))) + 1):
            writer.change(time, {refs[ref]: signals[ref][time - 1][1] for ref in signals})
    
        writer.close()

def plot_vcd(signals):
    fig, (ax1, ax2, ax3) = plt.subplots(3, 1, figsize=(10, 8))
    x_data = []
    y_data1, y_data2, y_data3 = [], [], []
    lines = [ax1.plot([], [])[0], ax2.plot([], [])[0], ax3.plot([], [])[0]]

    def init():
       for line in lines:
            line.set_data([], [])
        return lines

    def animate(i):
        x_data.append(i)
        y_data1.append(int(signals['sensor1'][i][1]))
        y_data2.append(int(signals['sensor2'][i][1]))
        y_data3.append(int(signals['sensor3'][i][1]))

        for j, (y_data, line, ax) in enumerate(zip([y_data1, y_data2, y_data3], lines, [ax1,     ax2, ax3])):
            line.set_data(x_data, y_data)
            ax.set_xlim(0, len(x_data))
            ax.set_ylim(0, max(14, max(y_data) + 1))
          
            if y_data[-1] >= 13:
                line.set_color('red')
                ax.set_facecolor('lightcoral')
                ax.set_title(f'Sensor {j+1}: Warning - High Value', color='red')
            else:
                line.set_color('blue')
                ax.set_facecolor('white')
                ax.set_title(f'Sensor {j+1}', color='black')
    
        return lines

    ani = animation.FuncAnimation(fig, animate, init_func=init,     frames=len(next(iter(signals.values()))), interval=100, blit=True)
    plt.show()


input_vcd = 'C:/intelFPGA/18.1/graph_plot.vcd'
signals = read_vcd(input_vcd)

output_vcd = 'C:/intelFPGA/18.1/graph_plot_filled.vcd'
write_vcd(signals, output_vcd)

`

signals_filled = read_vcd(output_vcd)
plot_vcd(signals_filled)
enter image description here

I tried using if instead of if else in the conditional statement and modified the process of loading the vcd file, but there was no significant difference.