I am having difficulty changing between two states. Basically there is a day and night scene with a button in the upper right hand corner that you click on to [theoretically] switch back and forth between the two. I can get it to switch from day to night but can't get it to go back to day. I feel like I might have some functions in the wrong place. I have tried using the redraw() method in various places as well. Here's the code:

2. // Images
3. PImage dayTime;
4. PImage nightTime;
5. PImage dayBut;
6. PImage nightBut;
7. 
   
8. // Coordinates
9. int butDayX, butDayY;
10. int butNightX, butNightY;
11. 
    
12. // Booleans
13. boolean isNight = false;
14. boolean overDay = false;
15. boolean overNight = false;
16. 
    
17. void setup() {
18.   size(750, 500);
19.   
20.   // Load Images
21.   dayTime = loadImage("day.jpeg");
22.   nightTime = loadImage("night.jpeg");
23.   dayBut = loadImage("dayBut.jpg");
24.   nightBut = loadImage("nightBut.jpg");
25.   
26.   // Button Positions
27.   butDayX = width - 125;
28.   butDayY = 25;
29.   butNightX = width - 125;
30.   butNightY = 25;
31.   
32. }
33. 
    
34. void draw() {
35.   if(isNight) {
36.     drawNight();
37.   }
38.   if(!isNight) {
39.     drawDay();
40.   }
41. }
42. 
    
43. // Update
44. void update(int x, int y) {
45.   if(isNight) {
46.     if(overDay(butDayX, butDayY, 100)) {
47.       isNight = false;
48.     }
49.   }
50.   if(!isNight) {
51.     if(overNight(butNightX, butNightY, 100)) {
52.       isNight = true;
53.     }
54.   }
55.   
56. }
57. 
    
58. // Change to Day Scene from Button Click
59. boolean overDay(int x, int y, int size) {
60.   if(mousePressed && mouseX >= x && mouseX <= x+size &&
61.     mouseY >= y && mouseY <= y+size)
62.     {
63.       overDay = true;
64.       return true;
65.     }
66.     else
67.     {
68.       overDay = false;
69.       return false;
70.     }
71. }
72. 
    
73. // Change to Night Scene from Button Click
74. boolean overNight(int x, int y, int size) {
75.   if(mousePressed && mouseX >= x && mouseX <= x+size &&
76.     mouseY >= y && mouseY <= y+size)
77.     {
78.       overNight = true;
79.       return true;
80.     }
81.     else
82.     {
83.       overNight = false;
84.       return false;
85.     }
86. }
87. 
    
88. // Draw Night Scene
89. void drawNight() {
90.   image(nightTime, 0, 0);
91.   image(dayBut, butDayX, butDayY);
92. }
93. 
    
94. // Draw Day Scene
95. void drawDay() {
96.   image(dayTime, 0, 0);
97.   image(nightBut, butNightX, butNightY);
98. }
99. 
    
100. void mousePressed() {
101.   update(mouseX, mouseY);
102. }

Any help is greatly appreciated. Thanks in advance!